Title of Invention

PROCESS FOR PRODUCING (METH) ACRYLIC ACID COMPOUND

Abstract A process for producing (meth)acrylic acid or (meth)acrylic esters, which comprises a reaction step comprising vapor phase catalytic oxidation of propylene, propane or isobutylene and, if necessary, a reaction step comprising an esterification step, characterized in that at the time when a high boiling mixture (hereinafter referred to as a high boiling material) containing a Michael addition product, is decomposed in a decomposition reactor to recover (meth)acrylic acids, while forcibly imparting a liquid flow in the circumferential direction to a liquid reaction residue in the decomposition reactor, the liquid reaction residue is discharged. In a process for recovering a valuable substance by thermally decomposing the high boiling material containing the Michael addition product of (meth)acrylic acids, it is possible to transfer the decomposition residue from the decomposition reactor to the storage tank without clogging, whereby a long-term continuous operation is possible.
Full Text DESCRIPTION
PROCESS FOR PRODUCING (METH)ACRYLIC ACIDS
TECHNICAL FIELD
The present invention relates to an industrially
advantageous process for producing (meth)acrylic acids at
a high recovery rate, while reducing the amount of
industrial wastes, by decomposing byproducts such as
Michael addition products of (meth)acrylic acid or
(meth)acrylic esters, by-produced in a step for producing
(meth)acrylic acids, and recovering variable compounds
such as (meth)acrylic acid, (meth)acrylic esters and
alcohols.
In this specification, "(meth)acrylic acid" is a
general term for acrylic acid and methacrylic acid, and
it may be either one or both of them. Further,
"(meth)acrylic acids" is a general term for these acids
and (meth)acrylic esters obtainable from such acids and
alcohols, and the term is meant for one comprising at
least one of them.
BACKGROUND ART
a. As a method for decomposing Michael addition
products by-produced during production of acrylic acid or
acrylic esters, it is common to employ a thermal
decomposition method using no catalyst in the case of a
process for producing acrylic acid (JP-A-11-12222), while
in the case of a process for producing an acrylic ester,
a method is known to carry out the decomposition by
heating in the presence of a Lewis acid or a Lewis base
(JP-A-49-55614, JP-B-7-68168, JP-A-9-110791, JP-A-9-
124552, JP-A-10-45670). Further, as a decomposition
reactive system for Michael addition products, it is
common to employ a reaction distillation system wherein
the desired decomposed reaction product is distilled by
distillation while carrying out the decomposition
reaction. Further, a method is also known wherein
Michael addition products by-produced in a step for
producing acrylic acid, and Michael addition products by-
produced in a step for producing an acrylic ester, are
put together, followed by thermal decomposition. There
are a method for thermal decomposition by a reactive
distillation system in the absence of any catalyst (JP-A-
8-225486) and a method for decomposition by means of a
highly concentrated acid catalyst (JP-A-9-183753) .
In order to increase the recovery rate of acrylic
acid, an acrylic ester or an alcohol useful as a product
or as a raw material for a reaction, at the top of such a
decomposition reaction column, it is necessary to
increase the decomposition reaction temperature and to
suppress the bottom discharge amount, whereby there has
heretofore been a problem such that the bottom liquid
tends to be a highly viscous liquid; as the decomposition
temperature is high, an oligomer or polymer of acrylic
acid or an acrylic ester being an easily polymerizable
substance, is likely to form; and some of substances
contained in the raw material for the reaction tend to
precipitate, whereby a solid will deposit at the bottom
of the decomposition reaction column, a polymer is formed
due to a liquid contained in the deposit, and such a
deposit will flow into a liquid discharge line at the
time of an operational change thereby to cause sudden
clogging of the liquid discharge line; and thus, there
has been no appropriate method whereby the decomposition
reaction column can be operated constantly for a long
time. Especially when a solid has once deposited at the
bottom of a decomposition reaction column, an easily
polymerizable liquid occluded in the deposited solid
tends to be extremely polymerizable since it can not flow,
and the decomposition reaction temperature is relatively
high, thus leading to a phenomenon where the amount of
the deposit will be further increased by such
polymerization. Thus, it has been desired to cope with
this problem.
b. As an example to solve this problem, a method is
conceivable wherein the diameter of a pipe to transfer
the bottom liquid is reduced to transfer the liquid at a
high flow rate, but it has been impossible to adopt such
a method, since the pump for such a transfer is required
to be of a high pressure type, such being economically
disadvantageous as an industrial production method.
Further, a method is also conceivable wherein in order to
lower the viscosity of the bottom liquid, waste liquid
from the production step may be added or water may be
added afresh, but such will bring about a decrease of the
liquid temperature, whereby clogging tends to be rather
accelerated, or it tends to be required to add such water
in a large amount. Accordingly, it has been practically
impossible to adopt such a method.
C. On the other hand, as is well known, there is a
vapor phase oxidation method of propylene as a reaction
to form acrylic acid. For such a method of obtaining
acrylic acid by oxidizing propylene, there are a two step
oxidation process wherein oxidation to acrolein and a
next step of oxidation to acrylic acid, are carried out
in separate reactors, respectively, since the oxidation
conditions are different, and a process wherein oxidation
to acrylic acid is carried out directly by one step
oxidation.
Fig. 9 shows an example of a flowchart for forming
acrylic acid by two step oxidation, followed by a
reaction with an alcohol to form an acrylic ester.
Namely, propylene, steam and air are subjected to two
step oxidation via the first and second reactors packed
with e.g. a molybdenum-type catalyst to form an acrylic
acid-containing gas. This acrylic acid-containing gas is
contacted with water in a collection column to obtain an
aqueous acrylic acid solution, which is extracted in an
extraction column by adding a suitable extraction solvent,
whereupon the extraction solvent is separated in a
solvent separation column. Then, acetic acid is
separated in an acetic acid separation column to obtain
crude acrylic acid, and in a fractionating column, a
byproduct is separated from this crude acrylic acid to
obtain a purified product of acrylic acid. Further, this
acrylic acid (purified product) is esterified in an
esterification reaction column, and then, via an
extraction column and a light component separation column,
a crude acrylic ester is obtained. From this crude
acrylic ester, a byproduct (high boiling product) is
separated in a fractionating column to obtain a purified
product of an acrylic ester.
Here, depending upon the type of the acrylic ester,
there may be a case where the flow sheet will be as shown
in Fig. 10. In such a case, the byproduct is obtained as
bottoms in an acrylic separation column.
In the process for producing an acrylic ester in Fig.
10, acrylic acid, an alcohol, recovered acrylic acid and
a recovered alcohol are respectively supplied to an
esterification reactor. This esterification reactor is
packed with a catalyst such as a strongly acidic ion
exchange resin. An esterification reaction mixture
comprising a formed ester, unreacted acrylic acid, an
unreacted alcohol, formed water, etc., withdrawn from
this reactor, will be supplied to an acrylic acid
separation column.
From the bottom of this acrylic acid separation
column, the bottom liquid containing unreacted acrylic
acid is withdrawn and recycled to an esterification
reactor. A part of this bottom liquid is supplied to a
high boiling component separation column, whereby a high
boiling component is separated from the bottom, and this
is supplied to and decomposed in a high boiling component
decomposition reactor (not shown). The decomposition
product containing a valuable substance formed by the
decomposition will be recycled to the process. A place
in the process where the decomposition product is
recycled, varies depending upon the process conditions.
High boiling impurities such as polymers will be
discharged from the high boiling decomposition reactor to
the exterior of the system.
From the top of this acrylic acid separation column,
an acrylic ester, an unreacted alcohol and formed water
are distilled. A part of the distillate is recycled as a
reflux liquid to the acrylic acid separation column, and
the rest is supplied to an extraction column.
To this extraction column, water for extraction of
an alcohol is supplied. Water containing an alcohol,
flowing out of the bottom, will be supplied to an alcohopi
recovery column. The distilled alcohol will be recycled
to the esterification reactor.
A crude acrylic ester discharged from the top of the
extraction column will be supplied to a light boiling
component separation column, and a light boiling material
is withdrawn from the top and recycled within a process.
A place within the process where it is recycled, varies
depending upon the process conditions. The crude acrylic
ester having the low boiling material removed, will be
supplied to a purification column for an acrylic ester
product, whereby a high purity acrylic ester will be
obtained from the top. The bottom liquid contains a
large amount of acrylic acid and therefore is recycled
within the process. The place within the process where
it will be recycled, varies depending upon the process
conditions.
Further, in recent years, instead of a solvent
extraction method wherein recovery of acrylic acid from
the above aqueous acrylic acid solution is carried out by
means of an extraction solvent, an azeotropic separation
method is carried out wherein distillation is carried out
by means of water and an azeotropic solvent, so that from
the top of the azeotropic separation column, an
azeotropic mixture comprising water and the azeotropic
solvent, is distilled, and from the bottom, acrylic acid
is recovered.
Further, also practically used is a method wherein
acrylic acid is obtained by using propane instead of
propylene and using a Mo-V-Te type composite oxide
catalyst or a Mo-V-Sb type composite oxide catalyst. In
the case of methacrylic acid and a methacrylic ester,
isobutylene or t-butyl alcohol is employed instead of
propylene, and a purified product of methacrylic acid and
a purified product of a methacrylic ester are obtained
via a similar oxidation process and the subsequent
ssterification process.
Further, as a method for forming a (meth)acrylic
=ster (an acrylic ester or a methacrylic ester), a method
is practically employed wherein a (meth)acrylic ester of
a lower alcohol and a higher alcohol are subjected to a
bransesterification reaction by using e.g. an acid as a
catalyst, to produce a (meth)acrylic ester of the higher
alcohol. The crude (meth)acrylic ester obtained by this
transesterification exaction, i^ subjected to steps such
as catalyst separation"; Concentration and fractionation
to obtain a purified (meth)acrylic ester.
A useful byproduct such as a Michael addition
product, is contained in the fraction separated by
distillation and purification of the above-mentioned
2rude acrylic acid, the crude methacrylic acid, the crude
acrylic ester or the crude methacrylic ester.
Accordingly, this byproduct is decomposed to recover
(meth)acrylic acid or its ester, or the raw material
alcohol.
Heretofore, the methods as disclosed in the above a
have been known as methods for decomposing a Michael
addition product by-produced during production of acrylic
acid or an acrylic ester. Thus, heretofore, it has been
common to decompose a Michael addition product by-
produced during production of an acrylic ester thereby to
recover a valuable substance such as acrylic acid, an
acrylic ester or an alcohol. As such a decomposition and
recovery method, it has been common to employ a reactive
distillation system wherein distillation is conducted
while carrying out a decomposition reaction.
To carry out the reactive distillation system, a
reactor provided at its upper portion with a distillation
column, is employed. As such a distillation column, it
is common to employ a plate column provided internally
with various trays, or a packed column having various
packing materials packed, in order to bring about
fractionating effects. The plates may, for example, be
bubble cap trays, uniflux trays, flexible trays, ballast
trays, perforated trays (sieve trays), chimney trays,
ripple trays, dual flow trays or baffle trays. The
packing material may, for example, be a ring-type packing
material such as Raschig rings, spiral rings or pall
rigns, or a saddle type packing material such as Berl
saddle or interlock saddle, or others such as Goodloe
packing, Dixon ring, MacMahon packing, or a vertically
flat plate type regulated packing material.
However, in both production processes for acrylic
acid and an acrylic ester, the raw material to be
supplied to the step of decomposing the byproduct, is a
fraction obtained by concentrating a high boiling
component formed in the reaction system or purification
system. Further, acrylic acid and acrylic esters are
very easily polymerizable materials, and consequently,
the raw material for the decomposition reaction contains
polymers formed. Further, the decomposition reaction is
carried out at a high temperature, and therefore, there
will be a polymer formed during the decomposition
reaction. Accordingly, it is likely that a solid
substance is already present in the raw material to be
subjected to decomposition, and even when no solid
substance is present in the raw material, it may
precipitate fanew,j or there may be a solid substance to be
formed during the distillation separation operation or in
the decomposition step where a chemical reaction is
simultaneously carried out. And, adhesion, deposition or
accumulation of such a solid substance takes place on the
trays or at void spaces of the packing material in the
distillation column, whereby an increase of the
differential pressure, deterioration of the gas/liquid
contact state and further clogging, may, for example,
occur. Consequently, there has been a problem that such
tends to hinder to obtain a high recovery rate of a
valuable substance or tends to hinder a constant
continuous operation.
Accordingly, in both processes for producing acrylic
acid and the ester, it is desired to solve the above
problems and to develop a process for decomposing a
Michael addition product, whereby a high recovery rate
can constantly be obtained.
d. Further, in a method for recovering (meth)acrylic
acid or a (meth)acrylic ester by carrying out the
decomposition reaction of a Michael addition reaction
product by-produced during the process for producing
(meth)acrylic acid or a (meth)acrylic ester, if the
decomposition reaction temperature is made high in order
to obtain a high recovery rate for such (meth)acrylic
acid, a (meth)acrylic ester or an alcohol, an oligomer or
polymer of (meth)acrylic acid or a (meth)acrylic ester
being an easily polymerizable substance, will be formed.
To prevent such polymerization, it is suggested to add
molecular oxygen in addition to a polymerization
inhibitor such as hydroquinone, methoxyhydroquinone,
phenothiazine or hydroxylamine, to the decomposition
reactor (e.g. the above-mentioned JP-A-10-45670,
paragraphs 0012 and 0019).
However, if such a method is employed, there may
sometimes be a case where not only no adequate effect fori
preventing polymerization of (meth)acrylic acid or a
(meth)acrylic ester in the decomposition product by
oxygen is obtainable, but also polymerization may be
accelerated, and thus there may be a case where the above
decomposition reaction can not be constantly continued
over a long time.
e. Further, an acrylic acid-containing gas obtained by
vapor phase catalytic oxidation by molecular oxygen of
propylene and/or acrolein, usually contains maleic acid,
as one of byproducts^ in an amount of from about 0.2 to
1.6 wt%, based on acrylic acid. Maleic acid is a
dicarboxylic acid represented by HOCO-CH=CH-C02H and is
in an equilibrium state with a carboxylic anhydride
having one molecule of water dehydrated in its molecule
in its solution. Hereinafter, unless otherwise specified,
maleic acid and maleic anhydride will be together
represented by maleic acid. When an acrylic acid-
containing gas is collected by a solvent in the form of
an acrylic acid-containing solution, maleic acid will be
collected at the same time. The boiling point of maleic
acid is high as compared with acrylic acid, and in the
purification step by distillation, maleic acid will be
concentrated in the bottoms.
When two molecules of acrylic acid undergo Michael
addition, an acrylic acid dimer will be formed. There is
no means to prevent formation of such an acrylic acid
dimer in the acrylic acid solution, and the formation
speed increases as the temperature becomes high. Further,
a higher oligomer such as an acrylic acid trimer will
sequentially be formed by acrylic acid and an acrylic
acid dimer. In the purification step for acrylic acid,
an acrylic acid dimer (or oligomer) will be formed mostly
in the distillation column where heating is carried out,
particularly at the bottom portion where the temperature
is high, and the retention time is long.
In order to improve the recovery rate of acrylic
acid in the purification step, it is usual to recover
acrylic acid from the formed acrylic acid oligomer.
As a recovery method from an acrylic acid oligomer,
there may, for example, be a method wherein thermal
decomposition is carried out under reduced pressure in
the presence or absence of a catalyst, and acrylic acid
is recovered as a distilled gas or a distilled liquid, as
disclosed in JP-B-45-19281. In such a case, the
distilled gas and the distilled liquid of acrylic acid
contains a large amount of high boiling compounds other
than acrylic acid to be recovered, such as maleic acid.
In a case where the operation temperature is increased in
order to increase the recovery rate of acrylic acid, the
maleic acid concentration in the recovered acrylic acid
will also be increased.
As a method to reduce such maleic acid, in a method
as disclosed in JP-A-11-12222, a crude acrylic acid
containing from 3 to 10 wt% of maleic acid and other
acrylic acid oligomers, is introduced into an acrylic
acid recovery column, and acrylic acid is distilled from
the top, and the bottom liquid is thermally decomposed,
and such a bottom liquid is recycled to the recovery
column, whereby maleic acid can be reduced to a level of
from 0 to 3 wt%.
In such a thermal decomposition recovery method of
an acrylic acid oligomer, maleic acid as an impurity is
disposed as bottoms of the thermal decomposition reaction
apparatus or the distillation apparatus. At that time,
if the amount of maleic acid contained in the recovered
acrylic acid is large, the amount of maleic acid recycled
in the system will increase, whereby instruments and the
heat load in the purification step will increase. The
simplest method to prevent this, is to reduce the thermal
decomposition recovery amount of the acrylic acid
oligomer, but the recovery rate for acrylic acid in the
purification step will thereby be decreased, and the
economical efficiency will be deteriorated.
In order to accomplish improvement of the recovery
rate of acrylic acid and reduction of the recycling
amount of maleic acid, there is a method of adding a
distillation column as in the method disclosed in JP-A-
11-1222. However, since acrylic acid is an easily
polymerizable compound, it is common to carry out
distillation under reduced pressure to prevent
polymerization by lowering the operational temperature,
but as the boiling point of maleic acid is higher than
acrylic acid, even if the operation pressure is lowered,
an increase of the operational temperature can not be
avoided. This will not only facilitate clogging of the
distillation apparatus by polymerization, but also tends
to accelerate formation of an acrylic acid oligomer in
the acrylic acid recovered by thermal decomposition.
Further, in order to increase the vacuuming degree of the
distillation installation, the diameter of the
distillation column is increased, whereby the load during
the construction and operation will also increase.
Further, concentrated maleic acid is discharged from
the bottom. However, maleic acid is solid at room
temperature and thus has problems such that the viscosity
of the liquid tends to be high from the lower portion to
the bottom of the distillation column, and deterioration
in the separation ability due to fouling, or deposition
of a polymer or clogging is likely to result.
Such problems result as maleic acid being an
impurity is separated as a high boiling substance by
distillation.
In order not to include a step of concentrating
maleic acid by distillation and to improve the thermal
decomposition recovery efficiency of acrylic acid, it is
necessary to carry out, without imparting a large heat as
distillation, either ® reducing the maleic acid
concentration in the acrylic acid solution to be supplied
to the thermal decomposition reaction apparatus, or (2)
reducing maleic acid in the acrylic acid solution
recovered from the thermal decomposition reaction
apparatus.
f. Further, heretofore, in an installation for
producing acrylic acid or the like, it has been common to
carry out a pressure measurement by installing a high
pressure side detection portion of a liquid level meter
in direct connection to the main body of the instrument.
However, by a conventional method for installation of a
liquid level meter, a polymerization inhibitor to be used
for the preparation of an easily polymerizable compound
or a formed polymer, is supplied to the high pressure
side detection portion of the liquid level meter, and a
solid substance is likely to be accumulated, whereby an
error operation of the liquid level meter used to be
observed.
Accordingly, it used to be difficult to carry out
accurate measurement continuously by a liquid level meter,
whereby it has been difficult to carry out a constant
operation of the installation for a long period of time.
DISCLOSURE OF THE INVENTION
a. It is an object of the present invention to overcome
the problems in the conventional decomposition reaction
of a Michael addition product of acrylic acid or an
acrylic ester thereby not to let deposition remain in the
decomposition reaction column, to prevent formation of a
polymer in the decomposition reaction column and to
prevent sudden clogging of the discharge pipe, so that a
stabilized operation method is presented.
b. Further, it is an object of the present invention to
provide a method for decomposing a byproduct during
production of (meth)acrylic acids, whereby at the time of
recovering a valuable substance by decomposing, by a
reactive distillation system, a Michael addition product
by-produced in the process for producing (meth)acrylic
acid or a (meth)acrylic ester, adhesion, deposition or
accumulation of such a solid substance is prevented, a
high recovery rate of (meth)acrylic acid, a (meth)acrylic
ester and an alcohol can be constantly maintained, and a
constant continuous operation can be carried out for a
long period of time.
c. Further, it is an object of the present invention to
provide a method to eliminate recycling of maleic acid in
an acrylic acid purification system involving thermal
decomposition and recovery of an acrylic acid oligomer
formed in the distillation purification step of an
acrylic acid-containing liquid and to readily accomplish
the purification without a problem of polymerization of
acrylic acid or clogging of an equipment in the
purification step.
d. Further, it is an object of the present invention to
provide a method for installing a liquid level meter on
an installation for producing an easily polymerizable
compound, whereby accurate measurement can continuously
be carried out by preventing formation and accumulation
of a solid substance of the liquid to be measured at a
high pressure side detection portion of the liquid level
meter.
The present inventors have conducted various studies
to accomplish the above objects, and as a result, have
arrived at the present invention having the following
gists.
(1) A process for producing (meth)acrylic acids, which
comprises a method of decomposing in a decomposition
reactor a high boiling mixture formed as a byproduct
during the production of (meth)acrylic acids,
characterized in that the high boiling mixture contains a
Michael addition product having water, an alcohol or
(meth)acrylic acid added to a (meth)acryloyl group; while
forcibly imparting a liquid flow in the circumferential
direction to a liquid reaction residue in the
decomposition reactor, the liquid reaction residue is
discharged; and (meth)acrylic acid or a (meth)acrylic
ester is recovered.
(2) The process according to the above (1),
characterized in that the liquid flow in the
circumferential direction is imparted by stirring vanes
installed in the decomposition reactor.
(3) The process according to the above (1),
characterized in that the liquid flow in the
circumferential direction is imparted by a liquid
supplied from the exterior of the decomposition reactor.
(4) The process according to the above (3),
characterized in that the liquid supplied from the
exterior of the decomposition reactor is the high boiling
material supplied as raw material, or a return liquid of
the liquid reaction residue discharged from the
decomposition reactor.
(5) The process according to any one of the above (1) to
(4), characterized in that the liquid reaction residue is
intermittently discharged from the decomposition reactor.
(6) The process according to any one of the above (1) to
(5), characterized in that at the time of recovering a
valuable substance by carrying out distillation as well
as thermal decomposition of the high boiling mixture, the
distillation is carried out by means of a distillation
column which is internally provided with disk-and-donut
type trays.
(7) The process according to any one of the above (1) to
(6), characterized in that an oxygen-containing gas is
added to a distillate from the decomposition reactor.
(8) The process according to any one of the above (1) to
(7), characterized in that from a liquid to be supplied
to the thermal decomposition reactor or from a liquid
recovered from the thermal decomposition reactor, maleic
acid contained in said liquid, is precipitated and
separated.
(9) The process according to any one of the above (1) to
(8), characterized in that a liquid level meter is
installed on the thermal decomposition reactor, and a
high pressure side detection line of the liquid level
meter is connected to a liquid discharge line of the
decomposition reactor.
The above present invention has the following
preferred embodiments (a) to (f).
al. A process for producing (meth)acrylic acids, which
is a process for producing acrylic acid or (meth)acrylic
acid (these are hereinafter generally referred to also as
(meth)acrylic acid) or a (meth)acrylic ester
((meth)acrylic acid and a (meth)acrylic ester may
hereinafter generally referred to also as (meth)acrylic
acids), by a reaction step comprising vapor-phase
catalytic oxidation of propylene, propane or isobutylene,
and, if necessary, further by a reaction step comprising
an esterification step, characterized in that at the time
when a high boiling mixture (hereinafter referred to as a
high boiling material) containing a Michael addition
product, is decomposed in a decomposition reactor to
recover (meth)acrylic acids, while forcibly imparting a
liquid flow in the circumferential direction to a liquid
reaction residue in the decomposition reactor, the liquid
reaction residue is discharged.
a2. The process according to the above al, wherein the
liquid flow in the circumferential direction is imparted
by stirring vanes installed in the decomposition reactor.
a3. The process according to the above al or a2, wherein
the stirring vanes are anchor vanes, multistage puddle
vanes, multistage inclined puddle vanes or lattice vanes.
a4. The process according to the above al or a2, wherein
the structure of the stirring vanes is such that on a
rotary shaft vertically installed at the center portion
of the reactor, radial flow type vanes are attached in
two or more stages in the rotational axis direction, so
that vanes adjacent in the rotational axis direction are
in a positional relation to the rotational axis direction
such that their phases are displaced from each other by
not more than 90°, and the lowest portion of the upper
stage one of the vanes adjacent in the rotational axis
direction, is located below the highest portion of the
lower stage one.
a5. The process according to the above al, wherein the
liquid flow in the circumferential direction is imparted
by a liquid supplied from the exterior of the
decomposition reactor.
a.6. The process according to the above al or a5, wherein
the liquid supplied from the exterior of the
decomposition reactor is the high boiling material
supplied as raw material, or a return liquid of the
liquid reaction residue discharged from the decomposition
reactor.
bl. A process for producing (meth)acrylic acids, which
is a process for producing acrylic acid, methacrylic acid
or a (meth)acrylic ester by a reaction step comprising
vapor-phase catalytic oxidation of propylene, propane or
isobutylene, and, if necessary, further by a reaction
step comprising an esterification step, characterized in
that at the time when a high boiling mixture (hereinafter
referred to as a high boiling material) containing a
Michael addition product, is decomposed in a
decomposition reactor to recover (meth)acrylic acids, a
liquid reaction residue is intermittently discharged from
the decomposition reactor.
b2. The process according to the above bl, wherein the
discharge stop time is from 5 seconds to 5 minutes, and
the discharge time is from 2 seconds to 5 minutes.
b3. The process according to the above bl or b2, wherein
the liquid high boiling material is continuously supplied
to the decomposition reactor, and (meth)acrylic acids are
continuously discharged from the vapor phase,
cl. In a process which comprises introducing a byproduct
formed during production of (meth)acrylic acid and/or a
byproduct formed during production of a (meth)acrylic
ester into a reactor provided with a distillation column,
thereby to thermally decompose the byproduct and at the
same to carry out distillation for recovering a valuable
substance, a method for decomposing the byproduct formed
during production of (meth)acrylic acids, characterized
in that as said distillation column, a distillation
column which is internally provided with disk-and-donut
type trays, is used.
c2. The process according to the above cl, wherein the
byproduct formed during production of (meth)acrylic acid
is the bottom liquid of a fractionating column in the
final step for producing (meth)acrylic acid, and the
byproduct formed during production of the (meth)acrylic
ester is the bottom liquid of a fractionating column for
separating a high boiling fraction in a purification step
for the (meth)acrylic ester.
c3. The process according to the above cl or c2, wherein
the byproduct formed during production of (meth)acrylic
acid and/or the byproduct formed during production of a
(meth)acrylic ester contains a Michael addition product
having water, an alcohol or (meth)acrylic acid added to
a (meth)acryloyl group.
c4. The process according to any one of the above cl to
c3, wherein the thermal decomposition reaction
temperature is from 120 to 280°C, and the thermal
decomposition reaction time is from 0.5 to 50 hours,
dl. A process for decomposing a byproduct formed during
production of (meth)acrylic acids, which comprises
decomposing in a decomposition reactor a byproduct formed
during production of (meth)acrylic acid and/or a
byproduct formed during production of a (meth)acrylic
ester, and distilling the decomposed product from the
decomposition reactor, characterized in that oxygen or an
oxygen-containing gas is added to the distillate from the
decomposition reactor.
d2. The process according to the above dl, wherein the
byproduct formed during production of (meth)acrylic acid
is the bottom liquid of a fractionating column in the
final step for producing (meth)acrylic acid, and the
byproduct formed during production of the (meth)acrylic
ester is the bottom liquid of a fractionating column in
the final step for producing the (meth)acrylic ester, or
the bottoms of a separation column for (meth)acrylic acid.
d3. The process according to the above dl or d2, wherein
the byproduct to be decomposed, contains a Michael
addition product.
d4. The process according to any one of the above dl to
d3, wherein the gas containing oxygen is air or oxygen
diluted with an inert gas.
d5. The process according to any one of the above dl to
d4, wherein the gas containing oxygen is added to a
discharge line for a distillate from the decomposition
reactor, or to the top portion of the decomposition
reactor.
el. In a process for producing acrylic acid, which
comprises contacting with a solvent an acrylic acid-
containing gas obtained by catalytic oxidation of propane
or propylene, to collect acrylic acid in the form of an
acrylic acid-containing solution, and purifying acrylic
acid by distillation of the obtained acrylic acid-
containing solution, a method for recovering acrylic acid,
characterized in that the bottoms obtained from the
bottom of a fractionating column for acrylic acid, or a
liquid obtained by heating and concentrating such bottoms,
is supplied to a thermal decomposition reactor to
decompose an oligomer of acrylic acid in the liquid, and
the obtained acrylic acid is recovered in a purification
step, wherein from the liquid to be supplied to the
thermal decomposition reactor or from the liquid
recovered from the thermal decomposition reactor, maleic
acid contained in the liquid is precipitated and
separated.
e2. The process according to the above el, wherein the
composition of the liquid to be supplied to the thermal
decomposition reactor or the liquid recovered from the
thermal decomposition reactor, is adjusted to become a
solution comprising at least 70 wt% of acrylic acid, from
1.6 to 28 wt% of maleic acid and/or maleic anhydride and
water having a molar ratio of:
Water
---------------------------------(molar ratio) Maleic acid+Maleic anhydridex2
and maleic acid is precipitated at from 20 to 7 0°C within
a range of from 0.5 to 5 hours, followed by filtration
and separation.
e3. The process according to the above el or e2, wherein
at the time of the separation operation of maleic acid,
an aliphatic or aromatic hydrocarbon is added in a volume
ratio of from 1/2 to 4 times.
e4. The process according to the above e3, wherein the
hydrocarbon to be added, is a solvent to be used for
collecting the acrylic acid-containing gas, or an
azeotropic agent to be used for dehydration distillation
purification of acrylic acid.
fl. A method for installing a liquid level meter in a
case where a liquid level meter is installed at a place
where a liquid containing an easily polymerizable
compound is stored, in an installation for production of
the easily polymerizable compound, characterized in that
a high pressure side detection line of the liquid level
meter is connected to a discharge line for the liquid
stored.
f2. The method according to the above fl, wherein the
connection angle a between the high pressure side
detection line and the liquid discharge line is from 5 to
90°.
f3. The method according to the above fl, wherein the
dimensional ratio D2/Di is from 1 to 20 where Di is the
pipe diameter of the high pressure side detection line
and D2 is the pipe diameter of the liquid discharge line.
f4. The method according to the above fl, wherein the
liquid discharge line is connected to a distillation
column, a reflux tank of the distillation column, a
decomposition reaction column, a thin film evaporator, a
column top gas condensed liquid tank, a vertical storage
tank, a horizontal storage tank or a tank.
f5. The method according to any one of the above fl to
f4, wherein the high pressure side detection line and/or
the low pressure side detection line of the liquid level
meter, is heated or warmed.
f6. The method according to any one of the above fl to
f5, wherein the high pressure side detection line and/or
the low pressure side detection line of the liquid level
meter, is connected with an inlet for a gas and/or a
liquid.
f7. The method according to any one of the above f1 to
f6, wherein the easily polymerizable compound is
(meth)acrylic acid or its ester, and the liquid to be
measured by the liquid level meter, contains at least one
member selected from an acrylic acid dimer, (5-
(meth) acryloxypropionic acid esters, (3-alkoxypropionic
acid esters, (3-hydroxypropionic acid and (5-
hydroxypropionic acid esters.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows an example of the production line by
the thermal decomposition reaction (the spiral flow is
formed by a return liquid to the decomposition reactor).
Fig. 2 shows an example of the production line by
the thermal decomposition reaction (the spiral flow is
formed by the raw material liquid supplied to the
decomposition reactor).
Fig. 3 shows an example of the production line by
the thermal decomposition reaction (the spiral flow is
formed by stirring vanes).
Fig. 4 is a view showing the cross section in a
horizontal direction of the decomposition reactor A and
the positional relation for connection with the lines for
forming the spiral flow.
Fig. 5 is a view schematically showing a solid
substance accumulated at the bottom of the decomposition
reactor A (a cross-sectional view in the longitudinal
direction of the column).
Fig. 6 shows an example of the production line by
the thermal decomposition reaction.
Fig. 7(a) is a schematic cross-sectional view
showing a distillation column provided with flat plate
disks and doughnuts, suitable for carrying out the method
for decomposing a byproduct formed during the production
of (meth)acrylic acids according to the present invention.
Fig. 7(b) is an enlarged perspective view of the
essential portions of Fig. 7(a).
Fig. 8(a) is a schematic cross-sectional view
showing a distillation column provided with slanted plate
disks and doughnuts, suitable for carrying out the method
for decomposing a byproduct formed during the production
of (meth)acrylic acids according to the present invention.
Fig. 8(b) is an enlarged view of the essential
portions of Fig. 8(a).
Fig. 9 is an example of the flowchart for production
of acrylic acid and an acrylic ester.
Fig. 10 is another example of the flowchart for
production of an acrylic ester.
Fig. 11 is a flowchart for decomposition of a high
boiling liquid.
Fig. 12 is a view showing the entire installation
wherein the method for installing a liquid level meter of
the present invention is applied to a (high boiling
material) decomposition reaction column and a top gas-
cooled liquid tank in the production of acrylic acid.
Fig. 13 is a partially enlarged view showing a
liquid level meter installed on the (high boiling
material) decomposition reaction column of Fig. 11.
Fig. 14 is a partially enlarged view showing a
liquid level meter installed on the top gas-cooled liquid
tank of Fig. 11.
Explanation of reference symbols
A: Decomposition reactor B: Bottom pump
C: Heat exchanger for heating D: Stirring means
E: Deposition F: Intermittent discharge control valve
1: High boiling material supply line
2: Bottom liquid discharge line
2-1, 2-2: Residual liquid discharge lines
3: Supply line for heat exchanger for heating
3-2: Return line for heating
4: Reaction residue discharge line
5: Spiral flow-forming return line
6: Valuable substance recovery line
7: Heating medium supply line
8: Heating medium discharge line
31, 33: Distillation columns
31D, 33D: Bottoms discharge ports
32A, 34A: Disk trays 32B, 34B: Doughnut trays
35: Distributor
41: Decomposition reaction column 42,46: Pumps
43 : Heat exchanger for heating
44a: Column top gas line
44, 47: Heat exchangers 45: Cooled liquid tank
6A: (High boiling material)decomposition reaction column
6E: Column top gas-cooled liquid tank
Hi, H2: Liquid level meters
62: Bottom liquid discharge line
62a: Bottom liquid discharge short pipe
62b: Bottom liquid discharge conduit
65: Bottom liquid discharge line
65a: Bottom liquid discharge short pipe
65b: Bottom liquid discharge conduit
11, 13: High pressure side detection line
11a, 13a: High pressure side detection short pipes
lib, 13b: High pressure side detection conduits
12, 14: Low pressure side detection line
12a, 14a: Low pressure side detection short pipe
12b, 14a: Low pressure side detection conduits
a: Connection angle between high pressure side detection
line and liquid discharge line
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment a
This Embodiment a has been accomplished on the basis
of a discovery that in a decomposition reaction of a
Michael addition product of acrylic acid or an acrylic
ester, it is very effective to make the liquid flow at
the column bottom in the circumferential direction in
order to prevent accumulation of a solid substance at the
bottom of the decomposition reaction column and thereby
to avoid polymerization due to such accumulation.
1. (meth) acrylic acid and (meth)acrylic ester
The present invention can be applied to
decomposition treatment of a high boiling mixture (high
boiling material) obtained during production of
(meth)acrylic acid or a (meth)acrylic ester. For example,
it can be applied to a process for producing
(meth)acrylic acid by vapor phase catalytic oxidation of
propylene or isobutylene in the presence of a Mo-Bi type
composite oxide catalyst to form acrolein or methacrolein,
followed by vapor phase catalytic oxidation in the
presence of a Mo-V type composite oxide catalyst. In
such a case, the preliminary reaction to form mainly
acrolein or methacrolein by oxidizing propylene or the
like and the later reaction to form mainly (meth)acrylic
acid by oxidizing acrolein or methacrolein, may be
carried out in separate reactors, respectively, or such
reactions may be carried out in one reactor packed with
both the catalyst for the preliminary reaction and the
catalyst for the later reaction. Further, the present
invention is also applicable to a process for producing
acrylic acid by vapor phase oxidation of propane by means
of a Mo-V-Te type composite oxide catalyst or a Mo-V-Sb
type composite oxide catalyst. Further, it is also
applicable to a process for producing an acrylic ester by-
reacting an alcohol to (meth)acrylic acid.
A high boiling mixture (high boiling material)
obtained after separating the desired product in these
processes, is the object to be decomposed by the present
invention. As the acrylic ester, a Ci_8 alkyl or
cycloalkyl ester may be mentioned. For example, methyl
acrylate, ethyl acrylate, butyl acrylate, isobutyl
acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, 2-
hydroxyethyl acrylate, 2-hydroxypropyl acrylate or
methoxyethyl acrylate may be mentioned. Also with
respect to a methacrylic ester, esters similar to the
above may be mentioned.
Michael addition product
The Michael addition product contained in the high
boiling material as the object to be decomposed by the
present invention, is one having an active hydrogen
compound such as water, an alcohol or (meth)acrylic acid
ion-added to a carbon-carbon double bond of (meth)acrylic
acid or a (meth)acrylic ester. Specifically, the Michael
addition product in the case of producing acrylic acid,
may, for example, be an acrylic acid dimer (hereinafter
the dimer), an acrylic acid trimer (hereinafter the
trimer), an acrylic acid tetramer (hereinafter the
tetramer) or p-hydroxypropionic acid, as illustrated
below.
Dimer : H2C=CH-C (=0) -0-CH2-CH2-C (=0) -OH
Trimer: H2C=CH-C (=0)-0-CH2-CH2-C (=0) -0-CH2-CH2-C (=0) -0H
Tetramer: H2C=CH-C (=0) -0-CH2-CH2-C (=0) -0-CH2-CH2-
C(=0) -0-CH2-CH2-C(=0)-OH
(3-hydroxypropionic acid: HO-CH2-CH2-C (=0)-OH
On the other hand, the Michael addition product in
the case of producing an acrylic ester, may, for example,
be a Michael addition product of acrylic acid to the
above acrylic ester, specifically a (3-acryloxypropionic
ester (an ester of the dimer); a Michael addition product
of an alcohol, specifically an ester of the dimer, the
trimer or the tetramer, p-hydroxypropionic acid, a (3-
hydroxypropionic esters or a p-alkoxypropionic esters.
(3-acryloxypropionic ester: H2C=CH-C (=0)-0-CH2-CH2-
C(=0)-OR
p-alkoxypropionic ester: RO-CH2-CH2-C (=0)-OR
Ester of the trimer: H2C=CH-C (=0)-0-CH2-CH2-C (=0)-0-
CH2-CH2-C(=0)-OR
p-hydroxypropionic ester: HO-CH2-CH2-C (=0)-OR
p-hydroxypropionic acid: H0-CH2-CH2-C (=0)-OH
Also with respect to methacrylic acid and a
methacrylic ester, substantially the same as the above
will apply. Only the difference is that as a result of
substitution of hydrogen at the a-position for a methyl
group, propionic acid (ester) becomes isobutyric acid
(ester).
The high boiling material to be supplied to the
decomposition reactor is a high boiling mixture
containing the above Michael addition product. The
content of the Michael addition product may vary to a
large extent by the production process. However, it is
common to employ a high boiling material containing a
Michael addition product in an amount of from 1 to 90 wt%,
preferably from 2 to 7 0 wt%. The high boiling material
also contains a compound by-produced in the step of
producing (meth)acrylic acids or a material to be used as
an assisting agent in the process. Specifically,
(meth)acrylic acid, (meth)acrylic esters, maleic acid,
maleic acid esters, furfural, benzaldehyde, polymers,
oligomers, alcohols to be used as materials for producing
esters, or polymerization inhibitors, specifically,
copper acrylate, copper dithiocarbamate, a phenol
compound or a phenothiazine compound, may, for example,
be mentioned.
The copper dithiocarbamate may, for example, be a
copper dialkyldithiocarbamate such as copper
dimethyldithiocarbamate, copper diethyldithiocarbamate,
copper dipropyldithiocarbamate or copper
dibutyldithiocarbamate, a copper cyclic
alkylenedithiocarbamate such as copper
ethylenedithiocarbamate, copper
tetramethylenedithiocarbamate, copper
pentamethylenedithiocarbamate or copper
hexamethylenedithiocarbamate, or a copper cyclic
oxydialkylenedithiocarbamate such as copper
oxydiethylenedithiocarbamate.
The phenol compound may, for example, be
hydroquinone, methoxyhydroquinone (methoquinone),
pyrogallol, resorcinol, phenol or cresol. The
phenothiazine compound may, for example, be phenothiazine,
bis-(a-methylbenzyl)phenothiazine, 3,7-
dioctylphenothiazine or bis(a-
dimethylbenzyl)phenothiazine. In some cases, materials
other than the above-mentioned may be contained depending
upon the process, without adversely affecting the present
invention.
Process for producing (meth)acrylic acids
The above-mentioned high boiling material may, for
example, be obtained via a purification step such as
extraction or distillation after contacting a
(meth)acrylic acid-containing gas obtained by vapor phase
catalytic oxidation of propylene or acrolein, with water
or an organic solvent to collect (meth)acrylic acid in
the form of a solution. The process for producing a
(meth)acrylic ester, for example, comprises an
esterification reaction step of reacting (meth)acrylic
acid with an alcohol in the presence of an organic acid
or a cationic ion exchange resin or the like, as a
catalyst, and a purification step of carrying out
extraction, evaporation or distillation as a unit
operation to concentrate the crude (meth)acrylic ester
solution obtained by the reaction. Each unit operation
is suitably selected depending upon the raw material
ratio of (meth)acrylic acid to the alcohol in the
esterification reaction, the type of the catalyst to be
used for the esterification reaction or the physical
properties of the raw materials, reaction byproducts, etc.
Flowchart for the thermal decomposition reaction of the
high boiling material
The description will be made with reference to the
drawings. Fig. 1 is an example of the production line by
the thermal decomposition reaction of the present
invention. The high boiling material is supplied via a
line 1 to a decomposition reactor A. The supply to the
decomposition reactor A may be carried out continuously
or intermittently (semi-continuously), but continuous
supply is preferred. A valuable substance formed in the
decomposition reactor and a part of materials
constituting the high boiling material will be
continuously withdrawn in a gas state from the recovery
line 6 and will be returned to the production process, as
it is in the gas state or as cooled in a liquid state.
In a case where the decomposition reactor A is a column
type reactor, a part of the cooled liquid may be returned
as a reflux liquid to the top of the decomposition
reactor.
The residual liquid will be withdrawn via a residual
liquid discharge line 2 and the bottom pump B, and a part
thereof is supplied to a heat exchanger C for heating via
a line 3 and returned to the decomposition reactor A.
The rest will be discharged out of the system via a line
4. The relation between the return liquid amount and the
discharge amount may suitably be set depending upon
various factors such as the heat balance at the heat
exchanger for heating and the retention time at the
decomposition reactor. The flow in the circumferential
direction (hereinafter sometimes referred to as a spiral
flow) in the decomposition reactor of the present
invention is formed by the return liquid of the line 5 in
Fig. 1. The line 5 is disposed in the tangent direction
of the main body of the decomposition reactor, and the
spiral flow will be formed in the reactor by the flow of
the liquid supplied from the line 5. The return liquid
amount of the line 5 is usually selected within a range
of from 0.2 to 5 times by weight, based on the amount of
the raw material supplied from the line 1. If the return
liquid amount is less than the above range, an adequate
spiral flow tends to be hardly formed. The return liquid
for heating, flowing through the line 3-2, is not related
to formation of the spiral flow, and its flow rate is
determined depending upon e.g. a heat balance.
Fig. 2 is one wherein the flow in the
circumferential direction is made by the raw material
liquid supplied to the decomposition reactor, and such is
carried out by the line 1. The line 1 is disposed in a
tangent direction of the main body of the decomposition
reactor, and the spiral flow will be formed in the
reactor by the raw material liquid supplied from the line
1. In this case, the line 1 is required to be controlled
so that the liquid surface will be below the liquid
surface of the reaction liquid retained in the
decomposition reactor.
Fig. 3 is an example of an apparatus to form the
spiral flow in the decomposition reactor by means of
stirring vanes.
The high boiling material is supplied from the line
1 to the decomposition reactor A. a valuable substance
and a part of materials constituting the high boiling
material, decomposed in the decomposition reactor A will
be withdrawn from a recovery line 6 and will be returned
to the production process in a gas state or as cooled in
a liquid state. In a case where the decomposition
reactor A is a column type reactor, the part of cooled
liquid may be returned as a reflux liquid to the top of
the decomposition reactor. The residual liquid will be
discharged from the line 4 out of the system. The heat
medium supply line 7 and the heat medium discharge line 8
are exemplary, and depending upon the type of the heat
medium, the positions of the supply line and the
discharge line may be changed.
The flow in the circumferential direction (the
spiral flow) in the decomposition reactor of the present
invention is carried out by the residual liquid-stirring
means D in Fig. 3. The stirring means D comprises
stirring vanes, a stirring shaft and a motor for stirring,
whereby the internal liquid of the decomposition reactor
is capable of forming a liquid flow in the
circumferential direction. The rotational speed of the
stirring vanes is usually suitably selected depending
upon the shape or the diameter of the vanes, so that the
forward end speed of the vanes will be usually from 0.2
to 5 m/sec. The residual liquid forming the spiral flow
will be withdrawn from the residual liquid discharge line
2-1 or 2-2. The residual liquid discharge line 2-1
represents an example wherein it is disposed in a tangent
direction of the main body of the decomposition reactor,
and the residual liquid discharge line 2-2 represents an
example wherein it is disposed at the center portion of
the decomposition reactor. In the case of the discharge
line 2-1, together with the stirring effect of the vanes,
a good spiral flow may be maintained.
Fig. 4 is a view showing the cross section of the
decomposition reactor A and the positional relation of
connection with the spiral flow-forming lines. The line
5 (spiral flow-forming return line 5) in Fig. 1 or the
line 1 (high boiling material-supply line 1) in Fig. 2,
is disposed in a tangent direction of the main body of
the decomposition reactor, whereby a flow in the
circumferential direction (a spiral flow) can be formed
within the decomposition reactor. Further, the residual
liquid discharge line 2-1 in Fig. 3 is disposed in a
tangent direction of the main body of the decomposition
reactor, whereby together with the stirring effect of
vanes, a good spiral flow can be maintained.
Fig. 5 is a view (column longitudinal cross-
sectional view) schematically showing a solid substance
accumulated at the bottom of the decomposition reactor A.
If the left and right accumulated products are joined,
the discharge port will be in a clogged state, whereby
withdrawal of the bottom liquid will be impossible, and
the bottom pump B may undergo cavitation.
Decomposition reaction of the high boiling material
The Michael addition product contained in the high
boiling material can be decomposed to a monomer
containing (meth)acrylic acid as the main component. In
a case where a (meth)acrylic ester is contained in the
high boiling material, it may be hydrolyzed to
(meth)acrylic acid and an alcohol, or may be recovered as
it is in the form of an ester without decomposition,
depending upon the conditions.
The temperature for the decomposition reaction is
adjusted to from 110 to 250°C, preferably from 120 to
23 0°C. In Fig. 1, the high boiling material is heated in
the heat exchanger C for heating, and the temperature is
controlled. Other than the one where a heater is
installed outside the decomposition reactor A, as shown
in Fig. 1, an inner coil type heater installed in the
decomposition reactor or a jacket type heater installed
around the decomposition reactor, is, for example,
available, and a heating device of any type may be used.
The retention time for the decomposition reaction
varies depending upon the composition of the high boiling
material, the presence or absence of the catalyst and the
decomposition reaction temperature. In a case where the
decomposition reaction temperature is low, it is a
relatively long time, such as from 10 to 50 hours, and in
a case where the decomposition reaction temperature is
high, it is from 30 minutes to 10 hours. The reaction
pressure may be either under a reduced pressure condition
or under an atmospheric pressure condition.
The decomposition reaction can be carried out by
using only the high boiling material as the object.
However, for the purpose of accelerating the
decomposition reaction, it may be carried out in the
presence of an acid catalyst or in the presence of water.
As the catalyst for the decomposition reaction, an acid
or a Lewis acid, such as sulfuric acid, phosphoric acid,
methanesulfonic acid, paratoluenesulfonic acid or
aluminum chloride, is mainly used. The catalyst and/or
water may preliminarily be mixed with the high boiling
material, or may be supplied to the decomposition reactor
A separately from the high boiling material. In a case
where a polymer, a polymerization inhibitor, a catalyst,
etc. are contained in the high boiling material, they
will usually remain and be concentrated in the
decomposition residue without being decomposed.
Structure of the decomposition reactor
The structure of the decomposition reactor A may be
any structure such as a column type or a tank type. In
the case of a column type reactor, trays or packing
materials which are commonly used in a distillation
column, may be installed as a content, whereby not only
the decomposition reaction but also a distillation
operation can be carried out, such being preferred. As
the packing material, a regular packing material such as
SULZER PACKING manufactured by SULZER BROTHERS LTD.,
SUMITOMO SULZER PACKING or MELLAPACK manufactured by
SUMITOMO HEAVY INDUSTRIES, LTD., GEMPAK manufactured by
GLITSCH, MONTZ PACK manufactured by MONTZ, GOODROLL
PACKING manufactured by TOKYO TOKUSHU KANAAMI K.K.,
HONEYCOMB PACKING manufactured by NGK INSULATORS, LTD. or
IMPULSE PACKING manufactured by NAGAOKA INTERNATIONAL
CORPORATION, may, for example, be used.
As an irregular packing material, INTALOX SADDLE
manufactured by NORTON, TELLERETTE manufactured by
Nittetu Chemical Engineering Ltd., PALL RING manufactured
by BASF, CASCADE MINI-RING manufactured by MASS TRANSFER
or FLEXIRING manufactured by JGC CORPORATION, may, for
example, be mentioned. Any one of such packing materials
may be used, or more than one of them may be used in
combination.
The trays may, for example, be bubble cap trays,
perforated plate trays, bubble trays, superflux trays or
max flux trays having a downcomer or dual trays or disk
and doughnut type trays having no downcomer. The trays
or the packing materials may be used in combination, or
no such content may be present in the decomposition
reactor.
In the present invention, the liquid flow in the
circumferential direction (the spiral flow) is one which
is generated forcibly, and such can be carried out by
supplying the high boiling material or the return liquid
of bottoms (the bottom liquid) from a tangent direction
of the reactor. In a case where a supply inlet from a
tangent direction is not present, the spiral flow is
formed by stirring vanes provided in the reactor. In
some cases, both means may be used in combination.
In the case of a tank type reactor provided with
stirring vanes, a baffle may be provided, as the case
requires. The stirring vanes may be of any type so long
as they are capable of generating a circumferential flow.
Specifically, anchor vanes, (at least one stage)
multistage paddle vanes, (at least one stage) multistage
inclined paddle vanes, lattice vanes, MAXBLEND vanes
(tradename, manufactured by SUMITOMO HEAVY INDUSTRIES,
LTD.), FULLZONE VANES (tradename, manufactured by SHINKO
PANTEC CO., LTD., etc. may be mentioned, and at least one
type may be used in at least one stage. FULLZONE VANES
are such that radial flow type vanes are attached in two
stages in a rotation axis direction on a rotational shaft
installed vertically at the center of the reactor, and
vanes adjacent in the rotational axis direction are in a
positional relation to the rotational axis direction such
that their phases are displaced from each other by not
more than 90°, and the lowest portion of the upper stage
one of the vanes adjacent in the rotational axis
direction, is located below the highest portion of the
lower stage one (see JP-A-7-33804) . Particularly
preferred as stirring vanes, are anchor vanes, lattice
vanes or FULLZONE VANES.
With respect to baffle plates (hereinafter baffles)
installed together with stirring vanes, there is no
restriction in the present invention. Any type may be
employed, or no baffles may be installed. Specifically,
a rod type, a plate type, a comb type may, for example,
be mentioned, and at least one type and at least one
member may be installed. It is particularly preferred to
install one rod type or one plate type.
Discharge of the residue of the decomposition reactor
The decomposition residue may be discharged from the
decomposition reactor by a suitable method. The bottom
discharge position of the decomposition reactor may be at
any place so long as it is the bottom end portion of the
column. It is preferably within a range of 1/2 of the
column diameter from the lowest portion of the bottom.
If it is located above the end portion, a solid substance
will be accumulated at the end portion. The residue is
stored in e.g. a tank and then recycled to incineration
treatment or a production process. On the other hand,
acrylic acid, methacrylic acid, an alcohol, etc. as
decomposition products of the Michael addition product or
the ester will be continuously discharged from the top
(the column top) of the decomposition reactor. They are
led to a purification system or recycled to a suitable
position in the production process.
Embodiment b
This Embodiment b has been accomplished on the basis
of a discovery that the decomposition reaction of the
Michael addition product of (meth)acrylic acids can be
carried out without clogging for a long time, by pulse
discharge i.e. intermittent discharge of the bottom
liquid instead of continuous discharge from the bottom of
the reactor. The reason as to why clogging can
effectively be prevented, is not clearly understood.
However, from the experimental facts, the present
inventors consider that the clogging in a pipe under a
constant flow, will be disturbed by the liquid flow by
intermittent flowing, and due to the disturbing effect of
the liquid flow, the clogging can extremely effectively
be suppressed in spite of the fact that the liquid flow
will be temporarily stopped.
"(Meth)acrylic acid and (meth)acrylic ester",
"Michael addition product" and "Process for producing
(meth)acrylic acids" are the same as in the case of
Embodiment a.
Flowchart for the production line by thermal
decomposition reaction of the high boiling material
Fig. 6 is an example of the production line by the
thermal decomposition reaction of the present invention,
which is the same as in the case of Embodiment a except
that C represents a heat exchanger for heating, F an
intermittent discharge control valve, and 3 a supply line
for the heat exchanger for heating.
The high boiling material is supplied to a
decomposition reactor A from a line 1. The supply to the
decomposition reactor A may be carried out continuously
or intermittently (semicontinuously), but continuous
supply is preferred. A valuable substance and a part of
materials constituting the high boiling material, formed
in the decomposition reactor is continuously withdrawn in
a gas state from a recovery line 6 and returned to the
production process, as it is in a gas state or as cooled
in a liquid state. In a case where the decomposition
reactor A is a column type reactor, a part of the cooled
liquid may be returned as a reflux liquid to the top of
the decomposition reaction column. The bottom liquid is
withdrawn from the line 2, and via a pump B, a part is
supplied to a heat exchanger C for heating and returned
to the decomposition reactor A. The rest will be
discharged out of the system from the line 4 via an
intermittent discharge control valve D as the gist of the
present invention. Reference numeral 5 represents a
transport pipe to a storage tank.
"Decomposition reaction of the high boiling
material" and "Structure of the decomposition reactor"
are the same as in the case of Embodiment a.
Intermittent discharge
In Embodiment b, the most significant feature is
that the decomposition residue is intermittently
discharged from the decomposition reactor. The
intermittent discharge is carried out by an intermittent
discharge control valve D. The closing time of the valve
D is usually from 5 seconds to 5 minutes, preferably from
10 seconds to 2 minutes, and the opening time of the
valve D is usually from 2 seconds to 5 minutes,
preferably from 3 seconds to 2 minutes. The opening
ratio of the control valve D (percentage of opening
time/(opening time+closing time)) is preferably within a
range of from 2 to 50%, more preferably from 5 to 30%.
If the closing time is shorter and the opening time is
longer than the above range, the clogging suppression
effect may not sufficiently be obtained due to an inertia
of the flow of the decomposition residue. If the closing
time is long and the opening time is short, clogging of
the pipeline is likely to take place due to an influence
of the static state of the liquid in the piping, such
being undesirable. In the continuous discharge (opening
rate: 100%), clogging of the pipe will take place as is
evident also from a Comparative Example hereinafter.
On the other hand, acrylic acid, methacrylic acid,
an alcohol, etc. as decomposition products of the Michael
addition product or the ester, will be continuously
discharged from the top of the decomposition reactor
(column top) . They will be led to a purification system,
or may be recycled to an appropriate position of the
production process.
Embodiment c
In Embodiment c, as trays for the distillation
column, disk and doughnut type trays are used, whereby
problems of adhesion, deposition and accumulation of the
solid substance have been solved. Namely, disk and
doughnut type trays are such that disk trays and doughnut
trays are alternately installed with a suitable distance,
and as shown in Figs. 7 and 8, the structure is very
simple, and the opening is extremely large, whereby a
solid substance is hardly precipitated or accumulated,
whereby it is possible to solve the problems of adhesion,
deposition and accumulation of the solid substance.
Accordingly, by using a distillation column equipped
with disk and doughnut type trays, decomposition of the
byproduct and recovery of a valuable substance during the
production of (meth)acrylic acids, can be carried out
constantly. The disk and doughnut type trays have a
structure which is extremely simple. Accordingly, as
compared with a distillation column employing
conventional trays or packing material, there is a merit
such that the production cost of the distillation column
and construction costs such as installation costs, can be
very low.
Now, a practical embodiment of the method for
decomposing the byproduct formed during production of
(meth)acrylic acids according to Embodiment c will be
described in detail. Firstly, with reference to Figs. 7
and 8, the construction of a distillation column equipped
with disk and doughnut type trays suitable for Embodiment
c will be described. Fig. 7(a) is a schematic cross-
sectional view showing a distillation column equipped
with flat plate type disks and doughnuts, and Fig. 7(b)
is an enlarged perspective view of the essential portions
of Fig. 7(a). Further, Fig. 8(a) is a schematic cross-
sectional view showing a distillation column equipped
with sloping plate type disk-and-doughnut trays, and Fig.
8(b) is an enlarged view of the essential portions of Fig.
8(a) .
The disk-and-doughnut type trays are such that a
plurality of disk-shaped trays and doughnut-shaped trays
are alternately disposed with a suitable distance in the
distillation column, and in distillation column 31 in Fig.
7, flat plate type disk-shaped trays 32A and doughnut-
shaped trays 32B are alternately disposed in the column.
Whereas, in the distillation column 3 in Fig. 8, sloping
plate type disk-shaped trays 34A and doughnut-shaped
trays 34B slanted in the liquid flow direction, are
alternately disposed. In the distillation columns 31 and
33 in Figs. 7 and 8, 31A and 33A are liquid inlets, and
31B and 33B are vapor inlets. Further, 31C and 33C are
vapor outlets, and 31D and 33D are bottom liquid outlets.
35 in Fig. 8 is a distributor (dispersing device).
The distance between the disk-shaped trays 32A and
34A and the doughnut-shaped trays 32B and 34B (L in Figs.
7 and 8) is preferably at least 250 mm in order to
suppress entrainment. If this distance L is excessively
large, the height of the distillation column will have to
be increased, and therefore, it is preferably at most 500
mm.
The plan view-shape of the disk-shaped tray 32A or
34A is preferably a perfect circle, and its center is
preferably located at the center of the distillation
column. Likewise, the plan view-shape of the doughnut-
shaped tray 32B or 34B is preferably a perfect circular
ring, and the outer periphery of the doughnut-shaped tray
32B or 34B is preferably closely in contact with the
inner wall of the distillation column 31 or 33.
The diameter of the disk-shaped tray 32A or 34A (Di
in Figs. 7 and 8) and the diameter of the opening of the
doughnut-shaped tray 32B or 34B (D2 in Figs. 7 and 8)
(hereinafter sometimes referred to as "inner diameter")
are suitable selected within a range of from 55 to 74% of
the inner diameter of the distillation column 31 or 33.
This size corresponds to a range of from 30 to 55% as
represented by the open area ratio in the distillation
column 31 or 33.
In order to avoid short path (short circuit) of the
down flow of the liquid in the distillation column 31 or
33, the diameter Di of the disk-shaped tray 32A or 34A is
preferably slightly larger than the inner diameter D2 of
the doughnut-shaped tray 32B or 34B.
With respect to the shape of trays, simple flat
plate type trays 32A and 32B as shown in Fig. 7 are
preferred. However, as shown in Fig. 8, with trays 34A
and 34B slightly slanted to the liquid flow direction, it
is possible to further suppress accumulation of a solid
substance. The sloping angle in such a case is not
particularly limited, but it is usually preferably set
within a range of from 5 to 45° against a horizontal
direction.
A method of installing the disk-shaped trays 32A and
34A and the doughnut-shaped trays 32B and 34B in the
distillation columns 31 and 33 may be any method. It may,
for example, be a method of fixing them by means of
supports extended from the walls of the distillation
columns, a method of welding them to the walls of the
distillation column, or a method wherein the respective
disk-shaped trays and doughnut-shaped trays are entirely
fixed to a vertical support and mounted in the
distillation columns in the form of an integral structure.
The number of plates of the disk-shaped trays and
doughnut-shaped trays to be installed in the distillation
column is not particularly limited and is suitably
selected so that the separation performance required for
the particular process, can be obtained. If the plate
number is too small, the distillation amount of the high
boiling component tends to be large, and the recycling
amount will increase, and the treating ability of the
decomposition reactor will decrease, such being
undesirable. On the other hand, if the plate number is
increased more than necessary, not only the construction
costs will increase, but also the distillation
concentration, at the top, of the polymerization
inhibitor contained in the raw material liquid decreases,
whereby an undesirable polymerization reaction of the
distillate is likely to take place, such being
undesirable. Accordingly, the disk-shaped trays and
doughnut-shaped trays to be installed, are preferably
selected within a range of from 5 to 20 plates (for this
plate number, one disk-shaped tray or doughnut-shaped
tray will be taken as one plate).
(Meth)acrylic acid in Embodiment c is preferably one
obtained by a catalytic vapor phase oxidation reaction of
propane, propylene, acrolein, isobutylene, t-butyl
alcohol or the like, and a gaseous oxidation reaction
product is rapidly cooled and quenched with water. Then,
separation of water and (meth)acrylic acid is carried out
by an azeotropic distillation method employing an
azeotropic solvent or by an extraction method employing a
solvent. Further, low boiling compounds such as acetic
acid are separated, and then a heavy component such as
the Michael addition product is separated to obtain high
purity (meth)acrylic acid. Otherwise, water and acetic
acid may be separated simultaneously by means of an
azeotropic agent. The above-mentioned Michael addition
product will be concentrated in the high boiling fraction,
and it is preferred that this fraction, i.e. usually the
bottom liquid of a fractionating column, is mixed with
the byproduct formed during production of a (meth)acrylic
ester, so that they are treated all together.
The (meth)acrylic ester in Embodiment c is not
particularly limited and may, for example, be methyl
(meth)acrylate, ethyl (meth)acrylate, n-butyl
(meth)acrylate, i-butyl (meth)acrylate, n-hexyl
(meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl
(meth)acrylate, methoxyethyl (meth)acrylate, i-nonyl
(meth)acrylate or i-decyl (meth)acrylate.
The Michael addition product is a byproduct to be
formed in a reaction step or a purification step in the
production of (meth)acrylic acid and a (meth)acrylic
ester, and it is a compound having (meth)acrylic acid,
acetic acid, an alcohol or water Michael-added at the a-
or (3-position of a compound having a (meth)acryloyl group
present in such a production process. The compound
having a (meth)acryloyl group present in the production
process, may, for example, be (meth)acrolein, a
(meth)acrylic acid, a carboxylic acid having a
(meth)acryloyl group, such as a p-acryloxypropionic acid
or a p-methacryloxyisobutyric acid (hereinafter both may
generally be referred to as the dimer) having
(meth)acrylic acid Michael added to such (meth)acrylic
acid, a (meth)acrylic acid trimer (hereinafter the
trimer) having (meth)acrylic acid Michael-added to such a
dimer, or a (meth)acrylic acid tetramer (hereinafter the
tetramer) having (meth)acrylic acid Michael-added to such
a trimer, or the corresponding (meth)acrylic ester having
such a carboxylic acid having a (meth)acryloyl group
esterified with an alcohol. Further, likewise, one
having (meth)acrylic acid Michael-added to (meth)acrolein
may also be contained. Specifically, the Michael
addition product of the present invention includes (3-
acryloxypropionic acid or (3-methacryloxyisobutyric acid,
and its ester and aldehyde compound (p-acryloxypropanal
or (3-methacryloxyisobutanal) , a (3-alkoxypropionic acid
and its ester, p-hydroxypropionic acid or p-
hydroxyisobutyric acid, and their esters and aldehyde
compounds, as well as dimers, trimers, tetramers, etc.,
and their (3-acryloxy compounds, p-acetoxy compounds, (5-
alkoxy compounds and p-hydroxy compounds. Further, a
compound having acetic acid Michael-added to a
(meth)acryloyl group, is present although it may be in a
very small amount.
In Embodiment c, as a method for producing a
(meth)acrylic ester, it is common to employ a method of
reacting an alcohol to (meth)acrylic acid for
esterification, or a method for producing an acrylic
ester of a higher alcohol, by reacting an acrylic ester
of a lower alcohol with a higher alcohol for
transesterification. Further, the production process may
be either a batch system or a continuous system. As a
catalyst for such esterification or transesterification,
an acid catalyst is usually employed.
The process for producing a (meth)acrylic ester
preferably comprises the reaction step and a purification
step for carrying out washing, extraction, evaporation,
distillation or the like as a unit operation to carry out
separation of the catalyst, concentration, purification,
etc. of the crude (meth)acrylic ester obtained in such a
reaction step. The starting material molar ratio of the
(meth)acrylic acid or the (meth)acrylic ester to the
alcohol in the reaction step may suitably be selected
depending upon the type and amount of the catalyst to be
used for the reaction, the reaction system, the reaction
conditions, or the type of the alcohol used as the raw
material.
The Michael addition product by-produced mainly by
the reaction will be concentrated at the bottom of the
distillation column (the fractionating column) to
separate a high boiling fraction. Accordingly, in the
present invention, this bottom liquid is, as the object
to be treated, subjected to thermal decomposition
together with the byproduct from the previous
(meth)acrylic acid production step, and the obtained
useful component will be recovered for the reaction step
for (meth)acrylic ester or a purification step.
Here, the distillation column to separate the high
boiling fraction may vary depending upon the type of the
(meth)acrylic ester to be produced or the process to be
used, but usually, it is one to separate (meth)acrylic
acid and the high boiling fraction, or one to separate a
(meth)acrylic ester and the high boiling fraction, or one
to separate (meth)acrylic acid, an alcohol and a
(meth)acrylic ester, and the high boiling fraction. The
present invention can be applied to all of them.
In the bottom liquid of the high boiling fraction-
separation column, the above-mentioned Michael addition
product is concentrated, but in addition, substantial
amounts of (meth)acrylic acid and/or a (meth)acrylic
ester are contained, and further, high boiling components
such as a polymerization inhibitor used in the process,
an oligomer or polymer formed in the process, high
boiling impurities in the raw material or their reaction
products, are contained. Further, in some cases, the
catalyst used for the esterification or
transesterification step may be contained.
As mentioned above, the Michael addition product by-
produced during the step for producing (meth)acrylic acid
will usually be concentrated at the bottom of a
distillation column (fractionating column) for separating
the product of (meth)acrylic acid from the heavy fraction.
In this bottom liquid, a substantial amount of
(meth)acrylic acid is also contained, and further, the
polymerization inhibitor used in the process, the
oligomer formed in the process or high boiling components
are also contained.
In Embodiment c, as the reactive distillation system
wherein the decomposition reaction of the Michael
addition product and distillation and recovery of the
valuable substance are simultaneously carried out, any
system such as a continuous system, a batch system, a
semi-batch system or an intermittent discharge system may
be employed, but a continuous system is preferred.
Further, the type of the reactor may be any of a
completely mixing type stirring tank reactor, a
circulation type completely mixing tank reactor or a
simple hollow reactor, without being restricted to any
particular type.
As the catalyst, a known Lewis acid or Lewis base
catalyst may be used, but simple thermal decomposition
employing no catalyst may be used. As conditions for the
decomposition reaction, the temperature is usually from
120 to 280°C, preferably from 140 to 240°C, and the
liquid retention time based on the discharge liquid, is
from 0.5 to 50 hours, preferably from 1 to 2 0 hours.
With respect to the reaction pressure, a condition is
preferably selected so that the majority of (meth)acrylic
acid, the (meth)acrylic ester, the alcohol, etc. to be
recovered, will be distilled at the reaction temperature.
In Embodiment c, a distillation column provided with
disk-and-doughnut type trays as shown in Fig. 7 or 8 is
installed to the reactor to carry out the reactive
distillation. This distillation column portion may be a
column directly connected to the reactor, or an
independent column of a system which is connected to a
vapor piping from the reactor and a liquid supply piping
from a distillation column, and thus the system is not
particularly limited. Further, the heating system for
the reactive distillation is not particularly limited and
may be a coil type in the reactor, an internal
multitubular heat exchanger type, an external jacket type
or an external heat exchanger type.
In a case where the reactive distillation is carried
out in a continuous system, the raw material may be
supplied to the distillation column portion or the
reactor portion at the bottom, but it is preferred to
supply it to the distillation column portion.
Further, in the present invention, the byproduct
formed during production of (meth)acrylic acid containing
the Michael addition product, and the byproduct formed
during production of a (meth)acrylic ester, may
separately be subjected to thermal decomposition
treatment, or they may be mixed and subjected to thermal
decomposition treatment.
Embodiment d
Embodiment d is one wherein oxygen or an oxygen-
containing gas is supplied directly to the distillate
containing the decomposition product formed by the
decomposition reaction of the above byproduct and one to
suppress polymerization of an easily polymerizable
compound in the decomposition product by the action of
such oxygen. As a result of various studies, it has been
found that polymerization of the easily polymerizable
compound in the decomposition product can be sufficiently
suppressed by the addition of such oxygen or an oxygen-
containing gas. This is considered to be attributable to
the fact that the oxygen added will increase the
polymerization-suppressing effect of the polymerization
inhibitor usually contained in the raw material for the
decomposition reaction.
In Embodiment d, the (meth)acrylic ester is not
particularly limited, but ones similar to those disclosed
in Embodiment c may be mentioned. Further, with respect
to the Michael-addition product, ones similar to those
disclosed in Embodiment c may be mentioned.
The feed liquid (hereinafter sometimes referred to
as the high boiling liquid) to be supplied to the
reaction decomposition column also contains substances
used or generated in the process for producing acrylic
acid or acrylic esters. Specifically, they are acrylic
acid, acrylic esters, maleic acid, maleic acid esters,
furfural, benzaldehyde, polymers, oligomers, alcohols to
be used as materials for production of esters, and a
polymerization inhibitor (copper acrylate, copper
dithiocarbamate, a phenol compound, a phenothiazine
compound, etc.).
The above copper dithiocarbamate may be ones similar
to those disclosed in Embodiment a. Further, the above
phenol compound may be ones similar to those disclosed in
Embodiment a.
Substances other than the above may sometimes be
contained depending upon the process.
(Meth)acrylic acid in Embodiment d is the same as
disclosed in Embodiment c. Further, the method for
producing a (meth)acrylic ester in Embodiment d, for
example, comprises a reaction step of reacting an alcohol
to (meth)acrylic acid for esterification by using a
cationic ion exchange resin as a catalyst, and a
purification step of carrying out washing, extraction,
evaporation, distillation or the like, to carry out
separation of the catalyst, concentration, purification,
etc. of the crude acrylic ester solution obtained in the
reaction step. The raw material molar ratio of the
(meth)acrylic acid or the (meth)acrylic ester to the
alcohol in the reaction step, the type and amount of the
catalyst to be used for the reaction, the reaction system,
the reaction conditions, etc., are suitably selected
depending upon the type of the alcohol raw material. The
Michael addition product by-produced mainly in the
esterification reaction step, will be concentrated as a
heavy fraction at the bottom of a reaction column for
recovering a variable component.
The byproduct formed during the production of
acrylic acid and the byproduct formed during the
production of an acrylic ester may be together decomposed.
In Embodiment d, any system of a continuous system,
a batch system, a semi-batch system or an intermittent
discharge system, may be employed for the reaction
process to carry out the decomposition reaction of the
Michael addition product, but a continuous system is
preferred. Also the type of the reactor is not
particularly limited, and any type such as a flow tubular
type reactor, a thin film flowing down type reactor, a
completely mixing tank type stirring tank reactor or a
circulation type completely mixing tank type reactor, may
be employed. To obtain useful components contained in
the decomposition reaction product, a method of obtaining
them by evaporation or distillation during the reaction
or a method of obtaining them by evaporation or
distillation after the decomposition reaction, may either
be employed. However, in order to obtain a high recovery
rate, the former reactive distillation system is
preferred.
In the case where the reactive distillation system
is employed, the reaction pressure depends substantially
on the after-mentioned reaction temperature, and a
pressure is employed such that the majority of useful
components such as acrylic acid, an acrylic ester, an
alcohol, etc., produced in the decomposition reaction and
contained in the raw material for the decomposition
reaction will be evaporated.
The catalyst may be selected from a Lewis acid, a
Lewis base, an inorganic acid such as sulfuric acid or
phosphoric acid, and an organic acid such as
methanesulfornic acid or p-toluenesulfonic acid. Water
may be supplied to the decomposition reaction column so
that decomposition may be carried out in the coexistence
of the high boiling fraction and water.
The concentration of the acid catalyst is preferably
from 0.1 to 1.0 wt%, particularly preferably from 0.2 to
0.8 wt%, based on the charged liquid.
The decomposition reaction temperature is preferably
from 110 to 250°C, particularly preferably from 120 to
230°C. The liquid retention time based on the discharge
liquid is preferably from 0.5 to 50 hours. Further, in a
case where the decomposition reaction temperature is
lower, it is preferably from 10 to 50 hours, and in a
case where the decomposition reaction temperature is
higher, it is preferably from 0.5 to 10 hours. Further,
in a case where the decomposition reaction is carried by
a continuous reaction, with respect to the reaction time,
the liquid retention time as calculated by the discharge
liquid may be regarded as the reaction time. For example,
in a case where the liquid capacity in the reactor is
500L, and the discharge liquid amount is lOOL/hr, the
retention time will be 5 hours.
To the distillate from the decomposition reaction
column, oxygen or an oxygen-containing gas (hereinafter
sometimes referred to as oxygen or the like) is added to
prevent its polymerization. As the oxygen or the like,
pure oxygen, a gas having oxygen diluted with an inert
gas, air, or a gas having air diluted with an inert gas,
may, for example, be employed. The inert gas may, for
example, be nitrogen, carbon dioxide, argon or neon. The
addition of the inert gas is to avoid formation of an
explosive gas. The inert gas is preferably present in an
amount of from 3.76 to 18.05 times by volume to oxygen,
and in the case of air, the inert gas is preferably
present in an amount of from 0.3 to 3 times by volume to
air. From the viewpoint of costs, it is apparent that
air is more inexpensive than oxygen. The oxygen or the
like is preferably added in a proportion of from 0.0001
to 0.01 volume ratio, particularly from 0.0005 to 0.005
volume ratio as calculated as oxygen to the distilled gas.
Further, in the present invention, the addition of
the oxygen or the like to the distilled gas of the
decomposition reaction column, may be carried out to the
line after discharge from the decomposition reaction
column, or the oxygen or the like may be added to the top
portion of the decomposition reaction column where the
distilled gas is substantially formed.
Fig. 11 is a flowchart showing the decomposition
reaction process. The high boiling liquid is supplied to
a decomposition reaction column 41 and thermally
decomposed. Here, this decomposition reaction column 41
may be provided with a stirrer to stir the liquid in the
column. Further, the decomposition reaction column 41
may be provided with a jacket for heating employing steam
or an organic heat medium as the heat source.
The bottom liquid in the decomposition reaction
column 41 is withdrawn by a pump 42, and a part thereof
is, via recycling line 43a, heated by a heat exchanger 43
for heating, and recycled, and the rest is discharged out
of the system.
The distillate formed by the decomposition reaction
is distilled from the top of the decomposition reaction
column 41, and after addition of oxygen or the like, via
a column top gas line 44a, cooled and liquefied by a heat
exchanger 44 and introduced into a cooled liquid tank 5.
Here, in a case where a reflux line is provided, the
cooled liquid tank 45 may be omitted. In Fig. 11, the
gas component in the cooled liquid tank 45 is led from
the cooled liquid tank 45 to a heat exchanger 7 and
cooled, whereby a valuable substance will be liquefied.
The non-condensed gas will be supplied to a valuable
substance-recovery installation or a vacuum installation
(not shown) . The liquid in the cooled liquid tank 45 is
withdrawn via a pump 46, and a part thereof will be,
after adding a polymerizing inhibitor, recycled via the
heat exchanger 44 to the cooled liquid tank 45, and the
rest will be taken out as the decomposition product.
This decomposition product will be returned to the
process for producing acrylic acid or an acrylic ester,
as mentioned above.
In the decomposition reactor 41, trays or a packing
material, which is commonly used in a distillation column,
may be provided. In such a case, it will be operated as
a decomposition reactive distillation column. As the
packing material, a regular packing material such as
SULZER PACKING manufactured by SULZER BROTHERS LTD.,
SUMITOMO SULZER PACKING manufactured by SUMITOMO HEAVY
INDUSTRIES, LTD., MELLAPACK manufactured by SUMITOMO
HEAVY INDUSTRIES, LTD., GEMPAK manufactured by GLITSCH,
MONTZ PACK manufactured by MONTZ, GOODROLL PACKING
manufactured by TOKYO TOKUSHU KANAAMI K.K., HONEYCOMB
PACKING manufactured by NGK INSULATORS, LTD. or IMPULSE
PACKING manufactured by NAGAOKA INTERNATIONAL CORPORATION,
or an irregular packing material such as INTALOX SADDLE
manufactured by NORTON, TELLERETTE manufactured by-
Nit tetu Chemical Engineering Ltd., PALL RING manufactured
by BASF, CASCADE MINI-RING manufactured by MASS TRANSFER
or FLEXIRING manufactured by JGC CORPORATION, may be
mentioned. Any one of these packing materials may be
employed, or more than one type may be used in
combination.
The trays may, for example, be bubble cap trays,
perforated plate trays, bubble trays, superflux trays,
max flux trays, etc. having a downcomer, or dual trays,
etc. having no downcomer. The trays or the packing
materials may be used in combination.
Further, no such a content may be provided in the
decomposition reaction column. In such a case, a
distillation column or the like may be installed, as the
case requires.
In a case where a stirring means is provided in the
decomposition reaction column 41, the stirring vanes may
be of any type, and for example, they may be anchor vanes,
(at least one stage) multistage paddle vanes, (at least
one stage) multistage inclined paddle vanes, as special
ones, MAXBLEND vanes (manufactured by SUMITOMO HEAVY
INDUSTRIES, LTD.), or FULLZONE VANES (manufactured by
SHINKO PANTEC CO., LTD.) . More than one type may be used
in more than one stage i.e. in multistages. Particularly
preferred are anchor vanes or lattice vanes.
Baffle plates (baffles) to be installed together
with the stirring vanes may be of any type. Specifically,
they may be of a rod type, a plate type or a comb type,
and more than one type, and more than one baffle may be
installed. It is particularly preferred to install one
rod type or one plate type. However, no baffle may be
provided.
The fraction rich in (meth)acrylic acid, a
(meth)acrylic ester and an alcohol, obtained by the
decomposition reaction, is recovered in its entire amount
for the step for producing an acrylic ester. The place
where the recovered fraction is to be recycled, is not
particularly limited. However, it contains a small
amount of a light fraction, and accordingly, it is
preferred to recycle it to a place prior to the step of
separating the light fraction.
Embodiment e
The invention of this Embodiment e relates to a
process for recovering acrylic acid. Particularly, in a
process which comprises contacting acrylic acid
containing maleic acid, particularly an acrylic acid-
containing gas obtained by a vapor phase catalytic
oxidation of propylene, with a solvent, to collect
acrylic acid in the form of an acrylic acid-containing
solution, distilling off a low boiling point component
from the acrylic acid-containing solution by azeotropic
distillation or direct distillation, then obtaining
acrylic acid by fractionation, while thermally
decomposing an oligomer of acrylic acid contained in the
bottoms of a distillation column, and recovering acrylic
acid and recycling it to a purification step, it relates
to a method for efficiently removing maleic acid as an
impurity from the liquid to be supplied to the thermal
decomposition reactor or from the distillate.
The invention of Embodiment e has been accomplished
on the basis of the discovery of the following fact by
the present inventors.
•Maleic acid formed together with acrylic acid by the
oxidation reactor is present in the form of a
dicarboxylic acid having two carboxyl groups, in an
aqueous solution, but in acrylic acid, it may have a form
of maleic anhydride having one molecule of water
dehydrated from its molecule. Maleic acid and maleic
anhydride are in an equilibrium state, and in the acrylic
acid solution to be supplied to the recovery apparatus of
the thermal decomposition reaction of an oligomer of
acrylic acid, the concentration of water as a low boiling
point component is low, whereby the equilibrium is
substantially shifted to maleic anhydride.
•When water is added to such a liquid, a part of
maleic anhydride turns into maleic acid in correspondence
with the amount of water added.
•In the column top liquid (or gas) of the thermal
decomposition reactor, water formed by the thermal
decomposition of 3-hydroxypropionic acid, etc. is present,
and a part of maleic anhydride will be reacted with this
water to form maleic acid.
•For the equilibrium reaction, it takes sometime, and
the equilibrium will be accelerated by heating.
•The solubility of maleic acid in acrylic acid is low
as compared with maleic anhydride, and maleic acid is
likely to undergo precipitation.
•The degree of precipitation depends on the
concentration of maleic acid or water in the liquid and
the operation temperature, and by an addition of a water-
insoluble solvent, precipitation will be accelerated.
•It is possible to facilitate precipitation and
separation by reducing the solubility by converting
maleic anhydride to maleic acid in the liquid to be
supplied to the thermal decomposition reactor for acrylic
acid or in the recovered liquid from the thermal
decomposition reactor.
And, by such a method, circulation in the
purification system of maleic acid involved in the
thermal decomposition and recovery of an oligomer of
acrylic acid formed in the step for distillation and
purification of the acrylic acid-containing liquid, can
easily be reduced by precipitation and solid-liquid
separation utilizing the chemical equilibrium of the acid
and the acid anhydride, whereby it is made possible to
recover acrylic acid without a problem of clogging by
polymerization.
Now, Embodiment e will be described in detail with
respect to each of items "Thermal decomposition reactor",
"Preparation of acrylic acid solution", "Reaction of
maleic acid", "Precipitation operation", and "Separation
of the precipitate".
Thermal decomposition reactor
The bottom liquid of the purification (product)
column for acrylic acid or the liquid obtained by
concentrating and heating the bottom liquid by a thin
film evaporator or the like, is used as the liquid to be
supplied, and heat decomposition of an oligomer of
acrylic acid is carried out within a temperature range of
from 12 0 to 22 0°C. The step for the thermal
decomposition reaction and the step for separating the
decomposed products may be carried out in the same
equipment such as a reactive distillation column, or in
separate equipments, such as a combination of a heating
tank and an evaporator. A catalyst may be used for the
thermal decomposition reaction. As a type of the
catalyst, a compound having a secondary or tertiary amino
group, or a tertiary phosphine may, for example, be
mentioned. However, the catalyst is not limited thereto.
Otherwise, the decomposition reaction may be carried out
in the absence of any catalyst.
Preparation of acrylic acid solution
The liquid to be supplied to the thermal
decomposition reactor or the recovered liquid from the
thermal decomposition reactor (the distillate) is to be
treated.
The concentration of maleic acid or/and maleic
anhydride in the recovered liquid is within a range of
from 1.6 to 28 wt%, preferably from 2.5 to 25 wt%. If
the concentration of maleic acid is low, the
precipitation tends to be difficult, and if the
concentration is too high, the loss of acrylic acid
increases at the time of separating the precipitated
maleic acid.
The concentration of water is as follows in a molar
ratio:
Water
-------------------------------------- Maleic acid + Maleic anhydride x 2
Particularly preferably, it is within a range of
[maleic anhydride] xO . 8^ [water] ^ [maleic
acid]xo.5+[maleic anhydride]. If the concentration of
water is too high, the precipitation amount of maleic
acid decreases, and the time required for precipitation
will be long.
The concentration of acrylic acid is at least 70 wt%.
If it is lower than this, the liquid nature will be
different, and there will be a case where the effect of
the present invention can not be obtained.
Reaction of maleic acid
In the solution, maleic acid and maleic anhydride
are present. As compared with maleic anhydride, maleic
acid has a low solubility in acrylic acid. Accordingly,
the larger the ratio of maleic acid/maleic anhydride in
the solution, the more efficient the removal by
precipitation.
To accelerate formation of maleic acid by the
reaction of maleic anhydride with water, the liquid
temperature may be raised to from 50 to 7 0°C. If the
temperature is raised beyond this range, the speed of the
formation of an oligomer of acrylic acid will be
accelerated, whereby not only the efficiency for heating,
decomposition and recovery of the oligomer will decrease,
but also polymerization of acrylic acid is likely to take
place, such being undesirable.
The reaction tank to be used is not particularly
limited. However, it is preferably provided with a
system to stir the solution, such as stirring vanes or an
external circulation by a pump, in order to prevent
polymerization in the tank.
In a case where the amount of maleic acid (not
including anhydride) in the solution exceeds 2 wt%, the
above operation may be omitted.
Precipitation operation
From the above-mentioned solution, maleic acid is
precipitated. The tank to be used for such precipitation
may be one used for the above operation or may be a
separate tank. The time required for the precipitation
is preferably within a range of from 0.5 to 5 hours
including the above operation. If the time is too short,
the precipitation efficiency tends to be poor. From the
viewpoint of the efficiency, the longer the required time,
the better. However, the instrument to be used is
required to be large, such being uneconomical.
The operation temperature is from 20 to 70°C,
preferably from 20 to 40°C. If the operation temperature
is too low, the cooling load will be increased, such
being uneconomical. Further, the melting point of
acrylic acid is 13°C, and freezing of acrylic acid may
occur. The higher the temperature, the more
polymerizable the acrylic acid, and the solubility of
maleic acid will increase, such being undesirable.
A solvent capable of forming double liquid layers
with water, may be added, whereby the precipitation
amount and the precipitation speed of maleic acid can be
increased. The solvent which may be employed for this
purpose, may, for example, be an aliphatic hydrocarbon
such as heptene or octene, an aromatic hydrocarbon such
as toluene, xylene or ethylbenzene, an ester such as
isopropyl acetate, or a ketone such as methyl isobutyl
ketone, but it is not limited thereto. More preferred is
a low polarity solvent such as an aromatic or aliphatic
hydrocarbon. The amount is preferably from 0.5 to 4
times by volume to the recovered acrylic acid solution.
If the amount is too small, no adequate effects for the
precipitation amount tends to be obtained. On the other
hand, an excessive amount of addition increases a load to
the process such as the size and ability of the
instrument, such being uneconomical. The same one as the
azeotropic agent to be used for the dehydration
distillation step may be employed, and in such a case,
the thermal load to remove the added solvent will not be
substantially increased.
Stirring may be carried out to prevent deposition on
the tank wall of crystals precipitated in the tank.
Further, crystals having a uniform particle size will be
precipitated by stirring, which makes the subsequent
separation step easy.
Separation of the precipitate
Separation of the precipitated maleic acid may be
carried out in the tank used for precipitation. However,
it is convenient to carry out the separation against the
liquid withdrawn from the precipitation tank, so that the
operation can be continuously carried out.
As a means for removing precipitated maleic acid in
the discharged liquid, a change-over strainer may, for
example, be convenient. However, such a means is not
limited thereto, and a usual solid-liquid separator may
be employed. A thickener, a precipitation tank, a
cyclone, a strainer, a centrifugal separator or the like
may be employed. The separated solid may be taken out by
opening the instrument. However, it may be dissolved by
a small amount of warm water and may be removed as waste
water. Depending upon the instrument, the separated
solid may continuously be discharged. The acrylic acid
solution having the precipitate removed, contains water
or an organic solvent added for the precipitation
operation and therefore preferably recycled to a
purification step prior to the purification column for
acrylic acid.
As a result of the above operation, the
concentration of maleic acid in the recovered acrylic
acid will be reduced to a level of from 1.4 to 3 wt%.
The content of this level will not adversely affect the
purity of the product, even if recycled to the
purification step.
Embodiment f
The invention of Embodiment f relates to a method
for installing a liquid level meter to be used for the
equipment for producing an easily polymerizable compound.
More particularly, it relates to a method for installing
a high pressure side detection portion of the liquid
level meter and is directed to a method for installing a
liquid level meter, whereby continuous operation of the
equipment has been made possible without clogging of the
detection portion of the liquid level meter.
Fig. 12 is a view showing the entire installation
wherein the method for installing a liquid level meter of
the invention of Embodiment f is applied to the (high
boiling material) decomposition reaction column and the
top gas-cooled liquid tank in the production of acrylic
acid, Fig. 13 is a partially enlarged view showing a
liquid level meter installed on the (high boiling
material) decomposition reaction column of Fig. 12, and
Fig. 14 is a partially enlarged view showing a liquid
level meter installed on the top gas-cooled liquid tank
of Fig. 12.
Firstly, with reference to Fig. 12, the installation
for the production of acrylic acid will be generally
described. 6A is a (high boiling material) decomposition
reaction column, and a supply line 61 is attached to the
(high boiling material) decomposition reaction column 6A.
6Bx is a bottom pump, and the inflow side of the bottom
pump 6Bi is connected to a bottom liquid discharge line
62 attached to the bottom of the (high boiling material)
decomposition reaction column 6A, and its outflow side is
connected to the decomposition residue discharge line 64.
6C is a heat exchanger for heating, and the inflow
side of the heat exchanger for heating is connected to
the supply line 63 for the heat exchanger for heating,
branched from the decomposition residue discharged line
64, and its outflow side is connected to a lower side
wall of the (high boiling material) decomposition
reaction column 6A by a line.
6D is a heat exchanger for cooling the column top
gas, and the inflow side of the heat exchanger 6D for
cooling the column top gas is connected to a
decomposition gas recovery line 66 attached to the top of
the (high boiling material) decomposition reaction column
6A, and its outflow side is connected to the inflow side
of a column top gas-cooled liquid tank 6E via a line.
Further, the outflow side of the column top gas-
cooled liquid tank 6E is connected to a column top gas-
cooled liquid discharge line 68 via a tank bottom liquid
discharge line 65 and a pump 6B2, and the column top gas-
cooled liquid is transferred by this line 68 to the next
installation.
A cooled liquid return line 69 branched from the
column top gas-cooled liquid discharge line 68, is
connected to the inflow side of the heat exchanger 6D for
cooling the column top gas.
6F is a heat exchanger for cooling a vent gas, and
the inflow side of the heat exchanger 6F for cooling a
vent gas, is connected to the column top gas-cooled
liquid tank 6E via a line. The vent gas flowing into the
heat exchanger 6F for cooling a vent gas, will be cooled
and, after a valuable substance in the gas is recovered,
will be led to a vent gas discharge line 67.
Hi and H2 are differential pressure type liquid level
meters, and the method for installing such liquid level
meters Hi and H2 is the essential feature of the present
invention.
Namely, the high pressure side of the differential
pressure type liquid level meter Hi is connected to the
bottom liquid discharge line 62 via a high pressure side
detection line 11, and the low pressure side of the
differential pressure type liquid level meter Hi is
connected to the lower side wall of the (high boiling
material) decomposition reaction column 6A via a low
pressure side detection line 12.
The high pressure side of the differential pressure
type liquid level meter H2 is connected to the tank
bottom liquid discharge line 65 via a high pressure side
detection line 13, and the low pressure side of the
differential pressure type liquid level meter H2 is
connected to the upper side of the column top gas-cooled
liquid tank 6E via a low pressure side detection line 14.
Now, specific examples of the method for installing
the above differential pressure type liquid level meters
Hi and H2 will be described in detail with reference to
Figs. 13 and 14.
In Figs. 13(1) and (2), 6A is the (high boiling
material) decomposition reaction column, and the liquid
stored at the bottom of the (high boiling material)
decomposition reaction column 6A is withdrawn out of the
column by the bottom liquid discharge line 62 constituted
by the bottom liquid discharge short pipe 62a attached to
the column bottom and a bottom liquid discharge conduit
62b.
Hi is the differential pressure type liquid level
meter, and the high pressure side of the differential
pressure type liquid level meter Hi is connected to
either the short pipe 62a or the conduit 62b constituting
the bottom liquid discharge line 62, by the high pressure
side detection line 11 constituted by a high pressure
side detection short pipe 11a and a high pressure side
detection conduit lib.
The connection angle a between the high pressure
side detection line 11 and the bottom liquid discharge
line 62 is from 5 to 90°, preferably from 10 to 90°.
If the connection angle is less than 5°, connection
is practically difficult, and if the connection angle
exceeds 90°, the solid substance in the liquid is likely
to flow into the high pressure side detection line 11,
such being undesirable.
The dimensional ratio D2/Di is from 1 to 20,
preferably from 1.3 to 10, where Di is the pipe diameter
of the high pressure side detection line, and D2 is the
pipe diameter of the liquid discharge line.
If the ratio D2/Di is less than 1, the solid
substance in the liquid is likely to flow into the high
pressure side detection line 11, such being undesirable,
and if D2/Di exceeds 20, detection of the liquid level
tends to be difficult.
The low pressure side of the differential pressure
type liquid level meter Hi is connected to the lower side
wall of the (high boiling material) decomposition
reaction column 6A by a low pressure side detection line
12 constituted by a low pressure side detection conduit
12b and a low pressure side detection short pipe 12a.
Fig. 13(1) is an example wherein the high pressure
side detection line 11 is connected to the vertical
portion of the bottom liquid discharge line 62, while Fig.
13(2) is an example wherein the high pressure side
detection line 11 is connected to a horizontal portion of
the bottom liquid discharge line 62.
In Figs. 14(1) and (2), 6E is the column top gas-
cooled liquid tank, and the liquid stored in the bottom
of the column top gas-cooled liquid tank 6E is withdrawn
out of the tank by the tank bottom liquid discharge line
65 constituted by a tank bottom liquid discharge short
pipe 65a attached to the tank bottom and a tank bottom
liquid discharge conduit 65b.
H2 is the differential pressure type liquid level
meter, and the high pressure side of the differential
pressure type liquid level meter H2 is connected to
either the short pipe 65a or the conduit 65b constituting
the tank bottom liquid discharge line 65, by a high
pressure side detection line 13 constituted by a high
pressure side detection short pipe 13a and a high
pressure side detection conduit 13b.
Further, the low pressure side of the differential
pressure type liquid level meter H2 is connected to the
upper side of the column top gas-cooled liquid tank E by
a low pressure side detection line 14 constituted by a
low pressure side detection conduit 14b and a low
pressure side detection short pipe 14a.
The connection angle a between this high pressure
side detection line 13 and the tank bottom liquid
discharge line 65, and the dimensional ratio D2/Di where
Di is the pipe diameter of the high pressure side
detection line 13, and D2 is the pipe diameter of the
tank bottom liquid discharge line 65, are acceptable, if
they satisfy the relation between the high pressure side
detection line 11 and the liquid discharge line 62, as
described in detail with reference to the above example
of Fig. 13.
Here, Fig. 14(1) is an example wherein the high
pressure side detection line 13 is connected to a
vertical portion of the tank bottom liquid discharge line
65, and Fig. 14(2) is an example wherein the high
pressure side detection line 13 is connected to a
horizontal portion of the tank bottom liquid discharge
line 65.
The above liquid discharge line is connected to a
place where the liquid containing an easily polymerizable
compound is stored, such as a distillation column, a
reflux tank for a distillation column, a decomposition
reaction column, a thin film evaporator, a column top
gas-cooled liquid tank, a vertical storage tank, a
horizontal storage tank or a tank, and the high pressure
side detection line of the liquid level meter is attached
thereto, so that the liquid level can be measured.
Further, the liquid level meter to be used in the
present invention may, for example, be a differential
pressure type liquid level meter, a glass gauge type or
tubular direct vision type liquid level meter or a
displacement type level indicator.
It is preferred that an injection inlet of a gas
and/or a liquid is connected to the high pressure side
detection line and/or the low pressure side detection
line of such a liquid level meter.
In a case where by some operational change, a solid
substance in the liquid flows into such a detection line,
it is possible to quickly discharge the solid substance
by the gas and/or the liquid. Such a gas and/or a liquid
may be supplied continuously or intermittently.
The gas to be used for this purpose is preferably
air nitrogen, carbon dioxide or the like, and as the
liquid, it is preferred to use the same liquid as the
liquid flowing in the liquid discharge line, such as
acrylic acid or an acrylic ester.
Further, it is preferred that such a portion is
heated or warmed to prevent deposition of a solid
substance in the liquid in the high pressure side
detection line and/or the low pressure side detection
line of the liquid level meter.
The easily polymerizable compound to be measured by
means of the method for installing a liquid level meter
of the present invention is effective when (meth)acrylic
acid or its ester is to be produced.
Further, as the liquid to be measured by the liquid
level meter, particularly effective is one containing at
least one type selected from an acrylic acid dimer, (3-
(meth) acryloxypropionic acid esters, (3-alkoxypropionic
acid esters, (3-hydroxypropionic acid and (3-
hydroxypropionic acid esters, by-produced during the
production of (meth)acrylic acid or its ester.
EXAMPLES
Now, the present invention will be described in
further detail with reference to Examples and Comparative
Examples, but the present invention is by no means
restricted by such Examples. Here, the analysis of the
composition of the high boiling material was carried out
in accordance with a usual method by means of gas
chromatograph provided with a flame ionization detector
(FID).
EXAMPLE al
A decomposition reaction of a high boiling material
was carried out by the installation shown in Fig. 1. As
the decomposition reactor, a column type reactor made of
Hastelloy C and having an outer diameter of 600 mm and a
length of 1800 mm, was used. As raw material, a high
boiling material having the following composition was
continuously supplied from the line 1 at a rate of 580
kg/hr.
Composition of high boiling material (raw material)
Butyl acrylate: 22 wt%
Butyl (3-butoxypropionate: 67 wt%
Butyl acryloxypropionate: 4 wt%
Butyl (3-hydroxypropionate: 2 wt%
Hydroquinone: 3 wt%
Methoxyquinone: 2 wt%
Further, as a decomposition reaction catalyst, a 1
wt% sulfuric acid aqueous solution was supplied at a rate
of 58 kg/hr (10 wt% to the raw material feed liquid), and
a decomposition reaction was carried out under a reaction
pressure of 100 kPa at a decomposition temperature of
190°C for a retention time of 1 hour.
From the line 6 at the top, a valuable substance
composed mainly of acrylic acid and butanol, was
recovered at a rate of 438 kg/hr, while a reaction
residue having the following composition was discharged
out of the system via the line 4 at a rate of 200 kg/hr.
Composition of reaction residue
Butyl acrylate: 11.0 wt%
Butyl (3-butoxypropionate: 68.5 wt%
Butyl acryloxypropionate: 2.0 wt%
Butyl p-hydroxypropionate: 0.3 wt%
Hydroquinone: 8.7 wt%
Methoxyquinone: 5.8 wt%
Butanol: 0.8 wt%
Sulfuric acid: 2.9 wt%
From the line 2 of the reactor A, the bottom liquid
was withdrawn at a rate of 35350 kg/hr, and from the line
5 (see Fig. 4) installed in a tangent direction to the
reactor A, 350 kg/hr of the bottom liquid was returned to
the reactor A by a flow rate control valve (not shown in
Fig. 1) installed on the line 5. The rest of 34800 kg/hr
was returned to the reactor A via the heat exchanger C
for heating and the return line 3-2 for heating. At that
time, a spiral flow was formed at the bottom of the
reactor A by the return liquid from the line 5. Further,
the pipe for the line 3 was 4B, and the pipe for the line
5 was 11/2(1.5)B.
After carrying out a continuous operation for 6
months, the operation was stopped, and the interior of
the decomposition reaction column was inspected. No
accumulation was observed at the bottom of the
decomposition reaction column. Further, during the
operation, there was no clogging in the transport pipe
for the reaction residue.
COMPARATIVE EXAMPLE al
An operation was carried out by the same apparatus
(Fig. 1) as in Example al except that with respect to the
connection of the line 5 to the decomposition reactor, it
was installed in the column center direction i.e. not in
the tangent direction. After the operation for 2 months,
cavitation occurred suddenly in the pump B. The
operation of the decomposition reaction column was
terminated, and the interior was inspected, whereby
accumulation of a solid substance was observed at the
bottom of the decomposition reaction column. The state
of the solid substance accumulated at the bottom of the
decomposition reaction column, is shown in Fig. 5.
EXAMPLE a2
Using the same apparatus (Fig. 1) as in Example al,
a high boiling material having the following composition
was continuously supplied from the line 1 at a rate of
580 kg/hr.
High boiling (raw material) composition
Acrylic acid: 45.3 wt%
Maleic acid: 10.0 wt%
Acrylic acid dimer
(acryloxypropionic acid): 42.4 wt%
Hydroquinone: 1.3 wt%
Phenothiazine: 1.0 wt%
A decomposition reaction was carried out under a
reaction pressure of 72 kPa at a decomposition
temperature of 190°C for a retention of 1 hours. From
the line 6 at the top, a valuable substance composed
mainly of acrylic acid was recovered at a rate of 449
kg/hr, while a reaction residue having the following
composition was withdrawn out of the system via the line
4 at a rate of 131 kg/hr.
Composition of reaction residue
Acrylic acid: 8.0 wt%
Maleic acid: 14.0 wt%
Acrylic acid dimer
(acryloxypropionic acid): 67.2 wt%
Hydroquinone: 5.8 wt%
Phenothiazine: 4.4 wt%
Oligomer and polymer: 0.6 wt%
The bottom liquid of the decomposition reaction
column was withdrawn from a 3/4B nozzle (line 2)
installed at the lowest position of the bottom portion
and supplied to the pump B. Via the pump B, it was
withdrawn from the line 4 at a rate of 131 kg/hr, while
to the line 3, it was supplied at a rate of 32000 kg/hr
as a return liquid to the decomposition reaction column
via the heat exchanger C for heating by a pipe having a
diameter of 4B.
On the other hand, the bottom liquid of the
decomposition reaction column was supplied as a return
liquid by the pump B from the line 5 to form the flow in
a circumferential direction in the decomposition reaction
column. The pipe diameter of the line 5 was 11/2(1.5)B,
and the flow rate was 400 kg/hr, and the such a control
was carried out by a flow rate control valve (not shown
in Fig.) installed on the line 5.
After carrying out a continuous operation for 6
months, the operation was stopped, and the interior of
the decomposition reaction column was inspected. No
accumulation was observed at the bottom of the
decomposition reaction column. Further, during the
operation, no clogging was observed in the transport pipe
of the reaction residue.
COMPARATIVE EXAMPLE a2
An operation was carried out by the same
installation as in Example a2 except that in Example a2,
the connection of the line 5 to the decomposition
reaction column was made in the center direction instead
of in the tangent direction.
After the operation for 7 0 days, cavitation occurred
suddenly at the pump B. The operation of the
decomposition reaction column was stopped, and the
interior was inspected, whereby accumulation of a solid
substance was observed at the bottom of the decomposition
reaction column. The state of the solid substance
accumulated at the bottom of the decomposition reaction
column, was as shown in Fig. 5.
EXAMPLE a3
A decomposition reaction of the same high boiling
material as in Example a2 was carried out by using a
decomposition reaction column (without a baffle) as shown
in Fig. 3 having anchor vanes installed as stirring vanes.
The decomposition reaction column has a jacket and has a
diameter of 600 mm and a height of 1000 mm, and the vane
diameter of the anchor vanes was 540 mm. An operation
was carried out under the same operation conditions as in
Example a2 by adjusting the rotational speed of the
anchor vanes to 20 rpm. Six months later, the operation
was stopped, and the interior was inspected, whereby no
accumulation of a solid substance was observed in the
column. Further, no clogging was observed in the
discharge line installed at the lowest portion of the
column bottom during the same period.
EXAMPLE bl
A decomposition reaction of a high boiling material
was carried out by the installation shown in Fig. 6. As
the decomposition reactor, a column type reactor made of
Hastelloy C and having an outer diameter of 600 mm and a
length of 18 00 mm, was used. As the raw material, a high
boiling material having the following composition was
continuously supplied from a line 1 at a rate of 580
kg/hr.
Composition of high boiling material (raw material)
Butyl acrylate: 22 wt%
Butyl (3-butoxypropionate: 69 wt%
Butyl acryloxypropionate: 4 wt%
Butyl (3-hydroxypropionate: 2 wt%
Hydroquinone: 2 wt%
Methoxyquinone: 1 wt%
Further, as a decomposition reaction catalyst, a 1
wt% sulfuric acid aqueous solution was supplied at a rate
of 58 kg/hr (10 wt% to the raw material supply liquid),
and a decomposition reaction was carried out under a
reaction pressure of 100 kPa at a decomposition
temperature of 190°C for a retention time of 1 hour.
From the top of the column, a valuable substance
composed mainly of acrylic acid and butanol, was
recovered at a rate of 449.5 kg/hr, and on the other hand,
from the column bottom, the reaction residue of the
following composition was intermittently withdrawn at a
rate of 188.5 kg/hr. Namely, the intermittent discharge
control valve D shown in Fig. 6 was operated for a
closing time of 7 5 seconds and an opening time of 5
seconds (the opening ratio: 6.3%).
The discharged liquid was sent to the reaction
residue storage tank installed in a distance of 80 0 m by
means of a pipe having a diameter of 3/4B (inner
diameter: 22.2 mm). A continuous operation was carried
out for 3 months, but no clogging was observed in the
transport pipe for the reaction residue. The results are
shown in Table 1.
Composition of the reaction residue
Further, the decomposition rates of the respective
components in the high boiling material were as follows.
Butyl [3-butoxypropionate: about 67 wt%
Butyl acryloxypropionate: about 83 wt%
Butyl (3-hydroxypropionate: about 74 wt%
Here, with respect to each component in the high
boiling material, the decomposition rate is defined by
[1-(discharged amount from the decomposition
reactor)/(supplied amount to the decomposition
reactor)]xl00 (%).
EXAMPLES b2 to b4
A reaction residual liquid obtained by the same
installation and operation as in Example bl, was sent to
the reaction residue storage tank in the same manner as
in Example bl except that the intermittent discharge time,
(opening ratio) was changed to the condition as shown in
Table 1. Under any condition, no clogging was observed
in the transport pipe as a result of the continuous
operation for 3 months. Further, the decomposition ratio
of the high boiling material was substantially the same
as in Example bl with respect to each component. The
results are shown in Table 1.
COMPARATIVE EXAMPLE bl
A reaction residual liquid obtained by the same
installation and operation as in Example bl, was sent
continuously to the same reaction residue storage tank as
in Example bl. From about the fifth day after initiation
of the operation, gradual decrease was observed in the
transport amount of the reaction residual liquid. A
mechanical shock was given to the pipe from the exterior,
clogging was partially and temporarily resolved, but
complete recovery of the transport amount was impossible.
Thereafter, the discharge amount continuously decreased,
and accordingly, the retention time in the decomposition
reactor gradually increased. As a result, the liquid
state of the reaction residue became highly viscous, and
on the 25th day, the operation of the decomposition
reactor had to be stopped. Further, the decomposition
ratio of the high boiling material during the steady
operation before stopping was substantially the same as
in Example bl with respect to each component. The
results are shown in Table 1.
EXAMPLES b5 to b8
Using the same apparatus as in Example bl, a
decomposition reaction was carried out by supplying a
high boiling material having the following composition as
the raw material at a rate of 580 kg/hr.
Composition of high boiling material (raw material)
Acrylic acid: 46.0 wt%
Maleic acid: 10.0 wt%
Acrylic acid dimer
(acryloxypropionic acid): 42.4 wt%
Hydroquinone: 0.9 wt%
Phenothiazine: 0.7 wt%
The conditions of the decomposition reaction were a
reaction pressure of 72 kPa, a decomposition temperature
of 190°C and a retention time of 1 hour, and no
decomposition catalyst was supplied.
From the column top, a valuable substance composed
mainly of acrylic acid was recovered at a rate of 449.5
kg/hr, while from the bottom, a reaction residue having
the following composition was intermittently discharged
at a rate of 130.5 kg/hr. Namely, the closing time and
the opening time of the intermittent discharge control
valve D as shown in Fig. 6, were set as shown in Table 2,
and the operation was carried out.
The discharged liquid was sent to the reaction
residue storage tank installed in a distance of 800 m by
means of a pipe having a diameter of 3/4B (inner
diameter: 22.2 mm). A continuous operation was carried
out for 3 months, whereby no clogging was observed in the
transport pipe for the reaction residue. Further, the
decomposition ratio of the acrylic acid dimer was about
72%. The results are shown in Table 2.
Composition of the reaction residue
Acrylic acid: 9.0 wt%
Maleic acid: 14.0 wt%
Acrylic acid dimer
(acryloxypropionic acid): 69.5 wt%
Hydroquinone: 4.0 wt%
Phenothiazine: 3.1 wt%
Oligomer and polymer: 0.4 wt%
COMPARATIVE EXAMPLE b2
A reaction residual liquid obtained by the same
installation and operation as in Examples b5 to b8, was
continuously sent to the same reaction residue storage
tank as in Examples b5 to b8. From about the 5th day
from the initiation of the operation, gradual decrease
was observed in the transport amount of the reaction
residual liquid to the storage tank. A mechanical shock
was given to the pipe from the exterior, whereby clogging
was partially and temporarily resolved, but complete
recovery of the transport amount was impossible.
Thereafter, the discharge amount continuously decreased,
and the retention time in the decomposition reactor
gradually increased. As a result, the liquid state of
the reaction residue became highly viscous, and the
operation of the decomposition reactor had to be stopped
on the 18th day. The results are shown in Table 2.
EXAMPLE cl
A decomposition reaction was carried out in
accordance with the present invention by using as raw
material a bottom liquid of a high boiling fraction
separation column in a process for producing methyl
acrylate, having the following composition:
Composition of the bottom liquid
Acrylate acid: 2 0 wt%
|3-hydroxypropionic acid: 1 wt%
Methyl (3-hydroxypropionate: 8 wt%
(3-acryloxypropionic acid: 8 wt%
Methyl (3-acryloxypropionate: 7 wt%
(3-methoxypropionic acid: 41 wt%
Methyl p-methoxypropionate: 12 wt%
Other high boiling components, etc.: 3 wt%
As a reactor portion at the bottom of the
decomposition reaction distillation column, a stirring
tank made of Hastelloy C having an internal diameter of
1000 mm and a height of 2000 mm, and a heat medium was
supplied to an external jacket to control the reaction
temperature at 200°C, and the reaction pressure was
maintained at 130 kPa. Further, at the upper portion of
this stirring tank reactor, a distillation column having
an internal diameter of 400 mm and a height of 400 0 mm
and further a condenser, were connected, whereby a
decomposition reaction was carried out by a reactive
distillation system.
In the interior of the distillation column, as shown
in Fig. 7, disk-shaped trays 2A having a diameter Di of
2 80 mm were installed in five stages with a distance of
600 mm from the uppermost portion to the lowermost
portion, and in-between thereof, doughnut-shaped trays 2B
with an opening having an inner diameter D2 of 2 60 mm
were installed in four stages with an equal distance.
The feeding position of the raw material liquid was
above the uppermost stage disk, and the above-mentioned
bottom liquid as the raw material was supplied at a rate
of 150 kg/hr. The liquid retention time was controlled
by the liquid level in the decomposition reactor, and
adjusted so that the retention time based on the
discharged liquid would be 10 hours. The operation was
continued for 1 month at a decomposition reaction
temperature of 2 00°C, whereby no increase of the
differential pressure was observed, and it was possible
to carry out the operation under a stabilized condition.
After the operation, the interior of the
distillation column was visually observed, whereby no
accumulation of a solid substance was observed. The
discharge amount of the decomposition residue during this
period was 76 kg/hr on average, and the composition was
analyzed by gas chromatography, and the results were as
follows.
Composition of the residue
Water: 0.2 wt%
Methanol: 0.2 wt%
Methyl acrylate: 0.3 wt%
Acrylic acid: 39 wt%
p-hydroxypropionic acid: 0.3 wt%
Methyl p-hydroxypropionate: 7 wt%
p-acryloxypropionic acid: 4 wt%
Methyl p-acryloxypropionate: 4 wt%
p-methoxypropionic acid: 31 wt%
Methyl p-methoxypropionate: 8 wt%
Other high boiling components, etc.: 6 wt%
COMPARATIVE EXAMPLE cl
A decomposition reaction was carried out for 1 month
by using the same apparatus, raw material and reaction
conditions as in Example cl except that as the
distillation column portion, a distillation column packed
with 2000 mm of a coil pack as a packing material instead
of the disk-and-doughnut type trays, was used. There was
no distinct difference from Example cl with respect to
the discharge amount or the composition of the residue,
but during this period, the pressure difference between
the top and the bottom of the distillation column
gradually increased, and upon expiration of 1 month, an
increase of differential pressure of 2.6 kPa was observed.
Further, after 1 month, the operation was stopped, and
the packing material was taken out and visually inspected,
whereby a substantial amount of a solid substance was
found to have deposited.
As is evident from the results of the above Examples
and Comparative Examples, when the process of the present
invention is employed, it is possible to carry out a
continuous operation in a stabilized condition without a
trouble of e.g. clogging or an increase in the
differential pressure and to prevent deposition or
accumulation of the solid substance.
EXAMPLE dl
A decomposition reaction of a high boiling liquid
was carried out by the installation as shown in Fig. 11.
The decomposition reactor had a column diameter of 10 00
mm and a column length of 2800 mm, and the material was
Hastelloy C. The composition of the high boiling liquid
was 22 wt% of butyl acrylate, 67 wt% of butyl (3-
butoxypropionate, 4 wt% of butyl acryloxypropionate, 2
wt% of butyl p-hydroxypropionate, 3 wt% of hydroquinone
and 2 wt% of methoxyquinone, and the liquid was supplied
at a rate of 580 kg/hr.
As a decomposition reaction catalyst, a 1 wt%
sulfuric acid aqueous solution was supplied in a weight
ratio of 10% to the supplied liquid, and the
decomposition reaction was carried out under a reaction
pressure of 100 kPa at a decomposition temperature of
190°C for a retention time of 1 hour, whereby a
decomposition gas comprising 45.8 wt% of butyl acrylate,
23 wt% of acrylic acid, 16 wt% of butanol, 11.9 wt% of
water, 2.9 wt% of butyl (3-butoxypropionate, 0.003 wt% of
hydroquinone, 0.007 wt% of methoquinone and 0.39 wt% of
others was obtained from the top of the decomposition
reaction column at a rate of 437.9 kg/hr. To the heat
exchanger for cooling the decomposition gas, the liquid
obtained by cooling the decomposition gas was returned at
a rate of 800 kg/hr.
As oxygen or the like, air at a rate of 3 Nm3/hr and
nitrogen as a diluting inert gas at a rate of 3 Nm3/hr
were supplied to the column top gas line 44a as shown in
Fig. 11.
After carrying out a continuous operation for 3
months, the operation was stopped, and the interior of
the decomposition reaction column was inspected. No
polymer was observed in the interior of the decomposition
reaction column or in the heat exchanger for cooling the
column top gas.
COMPARATIVE EXAMPLE dl
An operation was carried out by the same
installation as in Example dl except that as oxygen or
the like, air at a rate of 6 Nm3/hr and nitrogen as a
diluting inert gas at a rate of 6 Nm3/hr were supplied to
the recycling line 43a prior to the heat exchanger 43 for
heating, i.e. not to the column top gas line 44a.
After a continuous operation for 3 months, the
operation was stopped, and the interior of the
decomposition reaction column was inspected. A polymer
was observed in the interior of the decomposition
reaction column. No polymer was observed in the heat
exchanger 44 for cooling the column top gas.
COMPARATIVE EXAMPLE d2
An operation was carried out in the same manner as
in Comparative Example dl, except that air was supplied
at a rate of 3 Nm3/hr, and nitrogen as a diluting inert
gas was supplied at a rate of 3 Nm3/hr.
After a continuous operation for 3 months, the
operation was stopped, and the interior of the
decomposition reaction column was inspected. A polymer
was observed in the interior of the decomposition
reaction column, but the amount was about 1/3 of the
amount in Comparative Example dl. Further, a polymer was
observed also in the heat exchanger for cooling the
column top gas.
EXAMPLE d2
Decomposition of a high boiling liquid was carried
out by using the same apparatus as in Example dl. The
composition of the high boiling liquid was 5.3 wt% of
acrylic acid, 10 wt% of maleic acid, 42.4 wt% of an
acrylic acid dimer (acryloxypropionic acid), 1.3 wt% of
hydroquinone and 1 wt% of phenothiazine, and the liquid
was supplied at a rate of 580 kg/hr.
The decomposition reaction was carried out under a
reaction pressure of 72 kPa at a decomposition
temperature of 190°C for a retention time of 1 hour,
whereby a decomposition gas comprising 85.1 wt% of
acrylic acid, 8.7 wt% of maleic acid, 2.1 wt% of an
acrylic acid dimer (acryloxypropionic acid), 0.03 wt% of
hydroquinone and 4.07 wt% of others was obtained from the
top of the decomposition reaction column at a rate of
449.5 kg/hr. To the heat exchanger for cooling the
decomposition gas, the liquid obtained by cooling the
decomposition gas was returned at a rate of 500 kg/hr.
As oxygen or the like, air was supplied at a rate of
2 Nm3/hr to the column top gas line 44a as shown in Fig.
11.
After carrying out a continuous operation for 3
months, the operation was stopped, and the interior of
the decomposition reaction column was inspected. No
polymer was observed in the interior of the decomposition
reaction column or in the heat exchanger for cooling the
column top gas.
COMPARATIVE EXAMPLE d3
An operation was carried out by the same
installation as in Example dl except that as oxygen or
the like, air was supplied at a rate of 3 Nm3/hr to the
recycling line 3a.
After a continuous operation for 3 months, the
operation was stopped, and the interior of the
decomposition reaction column was inspected. A polymer
was observed in the interior of the decomposition
reaction column. Further, a polymer was also observed in
the heat exchanger for cooling the column top gas.
EXAMPLE el
Recovered liquid from the thermal decomposition reactor
Acrylic acid: 88 wt%
Acrylic acid dimer: 1.1 wt%
Acrylic acid trimer: 100 wt ppm
Maleic acid: 1.5 wt%
Maleic anhydride: 5.7 wt%
Water:
Water
------------------------------------(molar ratio)=0.34
Maleic acid + Maleic anhydride x 2
Operation
20 ml of a liquid having the above composition was
put into a test tube with a stopper and subjected to
horizontal shaking in an oil bath at 70°C for 2 hours
with an amplitude of 3 cm at a cycle of 1 second. Then,
toluene was added in an amount of two times by a volume
ratio, and the mixture was left to stand still at 3 5°C
for 1 hour, whereupon a precipitated solid was separated.
The separation of the solid was carried out at room
temperature by vacuum filtration employing a filter paper
of 1 u mesh. The separated solid contained mixed
crystals of 96% maleic acid and maleic anhydride, and
acrylic acid and very small amounts of impurities
impregnated therein. The concentration of maleic acid
including maleic anhydride after the removal of the solid
was 2.6 wt% as calculated by excluding the added toluene.
EXAMPLE e2
Separation of a solid was carried out under the same
conditions as in Example el except that no addition of
toluene was carried out. The concentration of maleic
acid including maleic anhydride after removing the solid
was 3.2 wt%.
EXAMPLE e3
An operation was carried out under the same
conditions as in Example el by adding 0.08 wt% of water
at the time of heating at 70°C. The amount of water at
that time was:
Water
---------------------------------(molar ratio)=0.38
Maleic acid + Maleic anhydride x 2
The concentration of maleic acid including maleic
anhydride after removing the solid was 2.4 wt%.
COMPARATIVE EXAMPLE el
An operation was carried out under the same
conditions as in Example e2 except that 3 wt% of water
was added at the time of heating at 7 0°C. The amount of
water at that time was:
Water
---------------------------------(molar ratio)=1.63
Maleic acid + Maleic anhydride x 2
No precipitation of a solid was observed, and the
concentration of maleic acid including maleic anhydride
was unchanged at 7.2 wt%.
EXAMPLE fl
A decomposition reaction of a high boiling liquid
was carried out by the installation as shown in Figs. 12
and 13.
The composition of the high boiling liquid was 22
wt% of butyl acrylate, 67 wt% of butyl p-butoxypropionate,
4 wt% of butyl acryloxypropionate, 2 wt% of butyl p-
hydroxypropionate, 3 wt% of hydroquinone and 2 wt% of
methoxyquinone, and the liquid was supplied at a rate of
580 kg/hr.
As a decomposition reaction catalyst, a 1 wt%
sulfuric acid aqueous solution was supplied in a weight
ratio of 10% to the supplied liquid, and the
decomposition reaction was carried out under a reaction
pressure of 10 0 kPa at a decomposition temperature of
190°C for a retention time of 1 hour, whereby from the
bottom, a reaction residue comprising 11.7 wt% of butyl
acrylate, 68.5 wt% of butyl p-butoxypropionate, 2 wt% of
butyl acryloxypropionate, 0.3 wt% of butyl p-
hydroxypropionate, 8.7 wt% of hydroquinone, 5.8 wt% of
methoxyquinone, 0.8 wt% of butanol and 2.9 wt% of
sulfuric acid, was obtained at a rate of 200.1 kg/hr and
discharged from the bottom.
The bottom liquid of the decomposition reaction
column was discharged from the bottom liquid discharge
line 62 attached to the lowermost position of the bottom
portion. The liquid level meter Hi at the bottom was a
differential pressure type liquid level meter and was
installed as shown in Fig. 13(1). The connection angle a
between the high pressure side detection line 11 and the
bottom liquid discharge line was set to be 45°.
After carrying out a continuous operation for 6
months, the operation was stopped, and the high pressure
side detection short pipe 11a and the high pressure side
detection conduit lib of the high pressure side detection
line 11 of the liquid level meter Hi, were inspected. As
a result of such inspection, no deposition was observed
in either one of them.
COMPARATIVE EXAMPLE fl
An operation was carried out under the same
conditions as in Example fl except that the high pressure
side detection line 11 of the differential pressure type
liquid level meter Hi was connected horizontally to the
lower side wall of the decomposition reaction column 6A.
After operation for 2 months, cavitation occurred
suddenly in the bottom pump Bi. Immediately, the
operation of the decomposition reaction column 6A was
stopped, and the interior was inspected, whereby it was
found that no liquid was present at the bottom portion of
the decomposition reaction column 6A, and the indication
of the liquid level meter Hi was erroneous.
The high pressure side detection short pipe 11a and
the high pressure side detection conduit lib of the high
pressure side detection line 11 of the liquid level meter
Hi were inspected, whereby the short pipe 11a and the
conduit lib were found to be clogged.
COMPARATIVE EXAMPLE f2
An operation was carried out under the same
conditions as in Example fl except that the high pressure
side detection line 11 of the differential pressure type
liquid level meter Hi was connected at a connection angle
a of 45° to the lower side wall of the decomposition
reaction column 6A.
After an operation for 3 months, cavitation occurred
suddenly in the bottom pump Bi. Immediately, the
operation of the decomposition reaction column A was
stopped, and the interior was inspected, whereby it was
found that no liquid was present at the bottom portion of
the decomposition reaction column A, and the indication
of the liquid level meter Hi was erroneous.
The high pressure side detection short pipe 11a and
the high pressure side detection conduit lib of the high
pressure side detection line 11 of the liquid level meter
Hi were inspected, whereby the short pipe 11a and the
conduit lib were found to be clogged.
EXAMPLE f2
An evaporation operation satisfying the following
conditions was carried out by using a thin film
evaporator.
As a raw material (crude acryl monomer) composition,
a mixture comprising 66.6 wt% of acrylic acid, 8.0 wt% of
maleic acid, 25.0 wt% of an acrylic acid oligomer, 0.5
wt% of hydroquinone and 0.5 wt% of phenothiazine, was
supplied at 85°C at a rate of 3000 kg/hr.
The operation was carried out under a column top
pressure of 9 kPa under a bottom pressure of 10 kPa at a
column top temperature of 95°C and a bottom temperature
of 98°C, whereby from the top of the column, 53% of the
supplied amount was withdrawn, and acrylic acid having a
purity of at least 88 wt%, was obtained.
From the bottom, a mixture comprising 41.1 wt% of
acrylic acid, 10.9 wt% of maleic acid, 46.16 wt% of an
acrylic acid oligomer, 0.92 wt% of hydroquinone and 0.92
wt% of phenothiazine, was discharged.
The bottom liquid of the thin film evaporator was
discharged by the bottom liquid discharge line attached
to the lowermost position of the bottom portion. The
liquid level meter at the bottom was a differential
pressure type liquid level meter and installed as shown
in Fig. 13(1). The connection angle a between the high
pressure side detection line 11 and the bottom liquid
discharge line was set to be 45°.
After carrying out a continuous operation for 6
months, the operation was stopped, and the high pressure
side detection short pipe 11a and the high pressure side
detection conduit lib of the high pressure side detection
line 11 of the liquid level meter, were inspected. As a
result of such inspection, no deposition was observed in
either one of them.
COMPARATIVE EXAMPLE f3
An evaporation operation was carried out under the
same conditions as in Example f2 except that the high
pressure side detection line 11 of the differential
pressure type liquid level meter was connected
horizontally to the lower side wall of the thin film
evaporator.
After operation for 1 month, cavitation occurred
suddenly in the bottom pump. The operation of the thin
film evaporator was stopped, and the interior was
inspected, whereby it was found that no liquid was
present in the thin film evaporator, and indication of
the liquid level meter was erroneous.
The high pressure side detection short pipe 11a and
the high pressure side detection conduit lib of the high
pressure side detection line 11 of the liquid level meter,
were inspected, whereby the short pipe 11a and the
conduit lib were found to be clogged.
INDUSTRIAL APPLICABILITY
a. According to the present invention, in a process for
recovering a valuable substance by heating and
decomposing a high boiling material containing a Michael
addition product of (meth)acrylic acids, the
decomposition reaction residue can be transported without
clogging from the decomposition reactor to a storage tank,
whereby a continuous operation for a long time will be
possible.
according to the process for decomposing a
;med during production of (meth)acrylic acids
it invention, at the time of recovering a
valuable substance such as (meth)acrylic acid, a
(meth)acrylic ester and an alcohol by thermally
decomposing by a reactive distillation system a byproduct
formed during production of (meth)acrylic acid and/or a
byproduct formed during production of a (meth)acrylic
ester, it becomes possible to carry out a continuous
operation under a stabilized condition while preventing
adhesion, deposition or accumulation of a solid substance
and while maintaining the recovery rate of the valuable
substance at a high level without bringing about a
problem such as clogging or an increase of the
differential pressure of the distillation column due to
deterioration of the gas-liquid contact state. Yet, in
the present invention, a distillation column having a
very simple structure may be adopted, whereby there will
be a merit that the construction costs will be very low
as compared with other distillation columns employing
trays or a packing material.
c. Further, according to the present invention, it is
possible to carry out decomposition treatment of a
Michael addition reaction product by-produced in the step
for producing (meth)acrylic acid and/or a (meth)acrylic
ester, under a stabilized condition, whereby
(meth)acrylic acid, a (meth)acrylic ester and an alcohol,
etc. can be recovered at a high recovery rate.
d. Further, according to the present invention, an
acrylic acid-containing gas obtained by catalytic
oxidation of propane or propylene, is contacted with a
solvent to collect acrylic acid as an acrylic acid-
containing solution, the obtained acrylic acid-containing
solution is distilled to purify acrylic acid, while an
acrylic acid oligomer from the bottom liquid containing
the acrylic acid oligomer, obtained from the purification
column, is thermally decomposed, and acrylic acid having
a small content of maleic acid, can be recovered
efficiently.
e. Further, if a method for installing a liquid level
meter of the present invention is adopted in the
installation for producing a easily polymerizable
compound, it is possible to prevent a solid substance
present in the liquid of the easily polymerizable
compound from flowing into a high pressure side detection
line of the liquid level meter. Accordingly, the
detection portion of the liquid level meter will not be
clogged by the liquid to be measured, whereby an accurate
continuous measurement by the liquid level meter will be
possible, whereby the installation can be operated over a
long period of time.
WE CLAIM:
1. A process for producing (meth)acrylic acids, which comprises a method of
decomposing in a decomposition reactor a high boiling mixture formed as a
byproduct during the production of (meth)acrylic acids, wherein a liquid level meter
is installed on the thermal decomposition reactor, and a high pressure side detection
line of the liquid level meter is connected to a liquid discharge line of the
decomposition reactor characterized in that the high boiling mixture contains a
Michael addition product having water, an alcohol or (meth)acrylic acid added to a
(meth)acryloyl group; while forcibly imparting a liquid flow in the circumferential
direction to a liquid reaction residue in the decomposition reactor, the liquid reaction
residue is discharged; and (meth)acrylic acid or a (meth)acrylic ester is recovered.
2. The process as claimed in Claim 1, wherein the liquid flow in the
circumferential direction is imparted by stirring vanes installed in the decomposition
reactor.
3. The process as claimed in Claim 1, wherein the liquid flow in the
circumferential direction is imparted by a liquid supplied from the exterior of the
decomposition reactor.
4. The process as claimed in Claim 3, wherein the liquid supplied from the
exterior of the decomposition reactor is the high boiling material supplied as raw
material, or a return liquid of the liquid reaction residue discharged from the
decomposition reactor.
5. The process as claimed in any one of Claims 1 to 4, wherein the liquid reaction
residue is intermittently discharged from the decomposition reactor.
6. The process as claimed in any one of Claims 1 to 5, wherein an oxygen-
containing gas is added to a distillate from the decomposition reactor.
7. The process as claimed in claim 2, wherein the stirring vanes are anchor
vanes, multistage puddle vanes, multistage inclined puddle vanes or lattice vanes.
8. The process as claimed in claim 2, wherein the structure of the stirring vanes
is such that on a rotary shaft vertically installed at the center portion of the reactor,
radial flow type vanes are attached in two or more stages in the rotational axis
direction, so that vanes adjacent in the rotational axis direction are in a positional
relation to the rotational axis direction such that their phases are displaced from each
other by not more than 90°, and the lowest portion of the upper stage one of the
vanes adjacent in the rotational axis direction, is located below the highest portion of
the lower stage one.
9. The process as claimed in claim 1, wherein the connection angle a between
the high pressure side detection line and the liquid discharge line is from 5 to 90°.
10. The process as claimed in claim 1. wherein the dimensional ratio D2/D1 is
from 1 to 20 where D1 is the pipe diameter of the high pressure side detection line
and D2 is the pipe diameter of the liquid discharge line.
11. The process as claimed in claim 1, wherein the liquid discharge line is
connected to a distillation column, a reflux tank of the distillation column, a
decomposition reaction column, a thin film evaporator, a column top gas condensed
liquid tank, a vertical storage tank, a horizontal storage tank or a tank.
12. The process as claimed in claim 1. wherein the high pressure side detection
line and/or the low pressure side detection line of the liquid level meter, is heated or
warmed.
13. The process as claimed in claim 1. wherein the high pressure side detection
line and/or the low pressure side detection line of the liquid level meter, is connected
with an inlet for a gas and/or a liquid.
14. The process as claimed in claim I, wherein the easily polymerizable compound
is (meth)acrylic acid or its ester, and the liquid to be measured by the liquid level
meter, contains at least one member selected from an acrylic acid dimer, ß-
(meth)acryloxypropionic acid esters, ß-alkoxypropionic acid esters, ß-
hydroxypropionic acid and ß-hydroxypropionic acid esters, formed as byproducts
when (meth)acrylic acid or its ester is produced.


A process for producing (meth)acrylic acid or
(meth)acrylic esters, which comprises a reaction step
comprising vapor phase catalytic oxidation of propylene,
propane or isobutylene and, if necessary, a reaction step
comprising an esterification step, characterized in that
at the time when a high boiling mixture (hereinafter
referred to as a high boiling material) containing a
Michael addition product, is decomposed in a
decomposition reactor to recover (meth)acrylic acids,
while forcibly imparting a liquid flow in the
circumferential direction to a liquid reaction residue in
the decomposition reactor, the liquid reaction residue is
discharged. In a process for recovering a valuable
substance by thermally decomposing the high boiling
material containing the Michael addition product of
(meth)acrylic acids, it is possible to transfer the
decomposition residue from the decomposition reactor to
the storage tank without clogging, whereby a long-term
continuous operation is possible.

Documents:

713-KOLNP-2004-(03-01-2012)-FORM-27.pdf

713-kolnp-2004-assignment.pdf

713-kolnp-2004-correspondence.pdf

713-kolnp-2004-examination report.pdf

713-kolnp-2004-form 13.pdf

713-kolnp-2004-form 18.pdf

713-kolnp-2004-form 3.pdf

713-kolnp-2004-form 5.pdf

713-KOLNP-2004-FORM-27.pdf

713-kolnp-2004-gpa.pdf

713-kolnp-2004-granted-abstract.pdf

713-kolnp-2004-granted-claims.pdf

713-kolnp-2004-granted-description (complete).pdf

713-kolnp-2004-granted-drawings.pdf

713-kolnp-2004-granted-form 1.pdf

713-kolnp-2004-granted-specification.pdf

713-kolnp-2004-reply to examination report.pdf

713-kolnp-2004-translated copy of priority document.pdf


Patent Number 241842
Indian Patent Application Number 713/KOLNP/2004
PG Journal Number 31/2010
Publication Date 30-Jul-2010
Grant Date 28-Jul-2010
Date of Filing 27-May-2004
Name of Patentee MITSUBISHI CHEMICAL CORPORATION
Applicant Address 33-8, SHIBA 5-CHOME, MINATO-KU, TOKYO 108-0014
Inventors:
# Inventor's Name Inventor's Address
1 YADA SHUHEI C/O MITSUBISHI CHEMICAL CORPORATION, 1, TOHO-CHO, YOKKAICHI-SHI, MIE 510-0848
2 OGAWA YASUSHI C/O MITSUBISHI CHEMICAL CORPORATION, 1, TOHO-CHO, YOKKAICHI-SHI, MIE 510-0848
3 SUZUKI YOSHIRO C/O MITSUBISHI CHEMICAL CORPORATION, 1, TOHO-CHO, YOKKAICHI-SHI, MIE 510-0848
4 TAKAHASHI KIYOSHI C/O MITSUBISHI CHEMICAL CORPORATION, 1, TOHO-CHO, YOKKAICHI-SHI, MIE 510-0848
5 TAKASAKI KENJI C/O MITSUBISHI CHEMICAL CORPORATION, 1, TOHO-CHO, YOKKAICHI-SHI, MIE 510-0848
PCT International Classification Number C07C 5/487
PCT International Application Number PCT/JP2002/12709
PCT International Filing date 2002-12-04
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2001-369636 2001-12-04 Japan
2 2001-385168 2001-12-18 Japan
3 2001-392058 2001-12-25 Japan
4 2001-371608 2001-12-05 Japan
5 2001-141162 2002-05-16 Japan